What is the most famous game in Canadian Chess history? For this talk, I'm going to exclude from consideration games played in Canada by two non-Canadians. We'll leave these possibilities for future talks:
I will consider games with at least one Canadian. So, the Canadian's opponent can be non-Canadian. Who are the most famous non-Canadian chess players? The World Champions, of course. So, let's consider games where Canadians beat future, reigning or past World Champions. Abe Yanofsky's win over future champion Mikhail Botvinnik in 1946 comes immediately to mind. In recent years, we are well aware of Pascal Charbonneau's win over Viswanathan Anand at the 2006 Olympiad; and Mark Bluvshtein's win over Veselin Topalov at the 2010 Olympiad.
I think games where players are representing Canada, such as at the Olympiads, are the most memorable. Let's take a look at a few of these situations from the beginning of Canada's chess history. We will see from this how my choice came to be so memorable.
In 1886, Nicholas MacLeod became the youngest ever Canadian Champion, when he was just past his 16th birthday - a record which still stands. He tied for first in 1887, and won the title again in 1888. In 1889, MacLeod played in the New York tournament, held to select a challenger to World Champion Wilhelm Steinitz. This marked the first time that a Canadian had unofficially represented us at a world event. It was a memorable occasion, although for the wrong reason: MacLeod set a record for most losses in one tournament, 31. By the way, you might think this was a very long time ago, but history is surprising: his daughter is still alive!
A Canadian representative was formally entered in an international event for the first time in 1895. The prestigious Hastings International Congress sent out invitations to the leading players in nations around the world. William Pollock represented Canada, and he impressed with wins over Steinitz, Tarrasch and Gunsberg.
Stephen Smith represented Canada at the Olympic Games Tournament, held in Paris, 1924. On behalf of Canada, he signed the document founding the World Chess Federation, FIDE.
In the 1930s, the driving force for chess in Canada was Bernard Freedman, a Toronto diamond merchant. He re-organized the CFC, and became Canada's representative to FIDE. In 1936, the Canadian Championship was held at the Canadian National Exhibition in Toronto. Freedman sponsored 11 year old Daniel Abraham Yanofsky to attend. 'Dan' or 'Abie', as he was known then, cleaned up in the junior and amateur side events and made newspaper headlines. He was clearly playing well above the level of all other children. Yanofsky, still a child, was ready to compete in a world dominated by older men.
Finally, in 1939, Canada officially entered two FIDE events, thanks to the organizational efforts and financial support of Freedman. Buenos Aires, Argentina, hosted the Olympiad team tournament among nations. Concurrently, the Women's World Championship tournament was held.
For Canada's Olympiad team, Freedman gave up his place as reserve board in favour of the 14-year old Abe Yanofsky. Further changes in the line-up moved Yanofsky up to Board 2, after 5-time Canadian Champion John Morrison. Canada's final Olympiad team was John Morrison, Abe Yanofsky, Haakon Opsahl, Walter Holowach and Abraham Helman.
The team met in New York for the trip south by boat. They were joined by Annabelle Lougheed, who was competing in the Women's Championship. She would later marry Freedman. Yanofsky warmed up by winning a tournament in New York.
The team enjoyed their trip as a vacation, stopping off in the Caribbean for a holiday. Two surprises awaited Abe in Argentina. First, immigration authorities would not let him in without a guardian. Luckily, an Argentine Chess Federation official took on this job. Second, he met an older brother living there, whom he didn't know existed!
In the final round of the preliminary round-robin, Canada's Board 1, John Morrison, sat out while Abe moved up.
Daniel Abraham Yanofsky - Alberto I. Dulanto
Canada - Peru, 8th Olympiad, Preliminaries, Board 1, Round 7, Buenos Aires, Argentina, 1939.08.30
French Defence (C10)
1. e4 e6 2. d4 d5 3. Nc3 Nf6 4. Bg5 dxe4
The two bishops that Black has in this variation do not compensate for White's greater freedom of action.  White's space advantage is more than enough compensation for the potential value of the two Black bishops. 
5. Nxe4 Nbd7
(A better continuation for Black is 5... Be7 6. Bxf6 (best ) Bxf6 followed by developing the knight at c6 ; or, maintaining the choice between developing the knight at c6 or d7. )
6. Nf3 Be7 7. Nxf6+ Nxf6
(Simpler is 7... Bxf6 as 8. Bxf6 (8. Qd2, 9. O-O-O with the better game ) Nxf6 gives Black a level game. )
(8. Ne5 (Capablanca) is refuted by 8... Qd5! (Spielmann), but an easier way than this variation to maintain the pressure is 8. c3, temporarily avoiding the manoeuvre played by Black. )
(The immediate 8... O-O gives White an advantage after 9. Qe2 c5 (9... b6 is prevented because of 10. Bxf6 Bxf6 11. Qe4 double attack on h7, a mate threat, and a8, where the rook is unprotected) 10. dxc5 Qa5+ 11. c3 Qxc5 12. O-O Rd8 13. Ne5) (8... b6 9. Ne5 Bb7 (9... Qd5 10. f3) 10. Bxf6 Bxf6 11. Bb5+) 
9. dxc5 Qa5+ 10. c3 Qxc5 11. O-O O-O 12. Re1
(12. Qe2 is an excellent alternative. ; this is a more effective way of limiting Black's chances, since it prevents 12... b6 because of 13. Bxf6 Bxf6 14. Qe4. )
Pinning White's B/d3 is ineffective. Doesn't guard a future B/d7 because of White's next. 
(12... h6 now, or next move at the latest, eliminating combinations based on the sham sacrifice at h7. )
13. Ne5 b6
(13... Bd7 (14. Bxf6 Bxf6 15. Nxd7 Rxd7 16. Bxh7+ Kxh7 17. Qxd7 ) and ... Be8, which would give Black a solid position, are stopped. ) (? [1,5] Overlooking White's threat. 13... h6 was essential, though after 14. Bxf6 (14. Bf4 b6 (14... Bd7 temporarily prevents the characteristic catastrophe that follows ) is still unsatisfactory because of 15. Qf3 Qd5 16. Nc6 ) Bxf6 15. Ng4 White still retains the initiative, e.g., 15... Bg5 16. Qf3. )
Yanofsky thought for a half-hour on this move, and calculated the subsequent play to after move 22. 
(Simpler than the strong alternative 14. Qf3. )
(Not 14... gxf6 15. Qh5. )
15. Bxh7+ Kf8
(15... Kxh7 16. Qh5+ Kg8 17. Qxf7+ Kh7 (17... Kh8 18. Re3 ++-- ) 18. Re3 and White mates quickly , e.g., 15... Bg5 19. Rh3+ Bh6 20. Rxh6+ Kxh6 21. Qg6#. )
16. Qh5 Bxe5
(16... Qc7 allows White to win either the exchange or two pawns by 17. Be4 Bb7 (17... Rb8 18. Nc6) 18. Nxf7 Bxe4 19. Nxd8.) (If Black plays the natural 16... g6 he loses after 17. Bxg6 fxg6 (17... Bxe5 18. Rxe5) 18. Qf3 Kg7 19. Ng4.) 
17. Rxe5 Qc7 18. Be4 Bb7
Black hopes to protect P/g7 by the possibility of 21 ... Rg8, "but White destroys this last hope with a pretty coup." 
(18... Rb8 19. Qh8+, 20. Qxg7 ++-- )
19. Bxb7 Qxb7 20. Qh8+ Ke7 21. Qxg7 Rg8
Black had gone this far in his calculations and felt quite happy since White is faced with mate or the loss of the queen. 
22. Rxe6+ !!
A direct hit from a well camouflaged piece. 
"! Not complicated, of course, but neat and decisive. The whole little game is characteristic of the incisive style of the young Canadian who was practically the only revelation of the Olympiad." 
22... Kxe6 23. Re1+ Kd6
Black has three other plausible continuations:
(23... Kf5 24. Re5+ Kf4 25. g3+ Kf3 26. Re3#) (23... Kd7 24. Qxf7+ Kc6 25. Re6+ Kd5 26. Re7+ discovered check winning the queen) (23... Kd5 24. Qd4+ Kc6 25. Qc4+ Kd6 (25... Kd7 26. Qxf7+) 26. Qf4+ Kc6 (26... Kd5 27. Qf3+ wins the queen by a skewer) (26... Kc5 27. Re5+ Kc6 28. Qf6+ Kc7 29. Qxf7+) (26... Kd7 27. Qxf7+) 27. Qf3+ Kc7 28. Qxf7+) 
24. Qf6+ Kc5
(24... Kd5) (24... Kd7  25. Re7+ ++--  (25. Qxf7+ ++-- )) both lose the queen quickly. 
25. Re5+ Kc4
(25... Qd5 26. b4+ Kc4 27. Qf4+ wins the queen. )
26. b3+ Kd3
(26... Kxc3 loses the queen on 27. Re7+.)
27. Qd6+ Kc2
(27... Kxc3 28. Re3+ Kc2 (28... Kb2 29. Re2+ #2 ) 29. Re2+ Kc1 (29... Kb1 30. Qd1#) (29... Kc3 30. Qd2#) 30. Qd2+ Kb1 31. Qb2#) 
28. Re2+ 1-0
White mates. 
This game attracted the attention of World Champion Alexander Alekhine, who followed all of young Yanofsky's remaining games and analyzed them with him!
Canada scored 11/24 in the 7 team Group 1 Preliminary, with Yanofsky going 4.5/7 (+3 =3 -1) on Board 2. Canada finished 5th, with only the top 4 qualifying for Group A in the Finals.
In the Group B Finals for the Copa Argentina, Canada scored 28/40 in the 11 team Round-Robin, tied with Iceland for first place. Canada was 2nd on tie-break. Yanofsky was the only Canadian to play every round. His result of 9.5/10 (+9 =1), including 9 wins in a row to finish the event, won him the prize for best individual result on Board 2 in the Group B Finals!
Yanofsky went on to become Canada's first Grandmaster.
Game notes are from  which uses ,  and  as sources; and .
Thanks to David J. Ross.