While the idea of 'buck' deriving from the beaver coin has some plausibility, I'm suspicious of it mainly because in the fair bit of reading I've done on the fur trade and related matters over the years, I don't believe I've ever come across that etymology.

Looking back at that 'Canadian Heritage' site, I see that there is some ambiguity in the wording - it says that the coin became known as a 'buck', and implies that that was because a male beaver pelt was known as a 'buck', but doesn't make either point directly. It leaves open the possibilities that a male beaver was not known as a 'buck', and that the coin may have been called a 'buck' for other reasons (such as that the term had already been applied to other currency?).