Well, for one thing, Canada didn't switch from pounds to dollars till 1858. That says something right there.

If you have a library card and still need convincin', you can view the Oxford English Dictionary online here for free:

http://www.oed.com/

There you'll find a verified, authentic, and unambiguous example of "buck" from a Sacramento, Calif., newspaper in 1856. The journalist didn't even feel he had to define the word.   

The evidence-based judgment of generations of OED editors - and everyone else who's seriously looked into this - is: "orig. and chiefly U.S."

No mention of beaver bucks in Colonial Canada, either.