""as a general rule it (buck) means specifically a male deer"".

Where is such a general rule written, as you seem to suggest? If it were so, Deer are not exclusive to the USA.

""And should we believe that only the pelts of male beavers ("buck beavers" presumably) were used as currency""?

I suspect this question would also logically apply to male deer pelts?


""My educated guess is that it only happened after the U.S. "buck" became generally familiar to Canadians.""

One persons guess is as good as anothers, as would the burden of proof/evidence, I guess:)