Canada, Fur trade tokens:
The first were the Northwest Company copper and brass tokens of 1820, which could be exchanged for goods in their west coast posts.
The Hudson's Bay Company did not issue tokens until 1854; these had the values of 1/8, 1/4, 1/2 and 1 made beaver.

Prior to these dates, if the transaction demanded currency, the coins of French Canada (Deners and sols) and British Colonies (Penny, etc.) were used (or monies of the parent countries).

None of these early coinages or their denominations were related in any way, or were ever referred to, as a "buck."

Canadian Heritage (Patrimoine canadien) is responsible for programs and policies relating to arts, culture, language, etc., etc., but does not have anything pertinent to this thread.

I don't know when the dollar was called a "buck" with any frequency in the U.S. (1890s?) but it is likely Canadians would have seen or heard that usage and used it soon thereafter.