I can't speak for all canadians, but I wouldn't boo any fighter or sports team.
And I wasn't hating on Yanks, I was stating that this appeared to be the reason for them booing some of the fighters, like GSP and the Japanese guy in the first bout.
And, as a I stated in the first post. I went to a KOTC match that was billed as a USA vs Canada tournament, held here in British Columbia, and there was no booing at all. The US fighters got cheered almost as loud as the canadians and got cheered loudly when one dude KO'ed a Canadian with an awesome flying knee.