You do know that sometimes in the hockey playoffs, American crowds boo the Canadian anthem, even though many of their players are Canadian, right?
I don't agree with booing other nation's anthems, nor something like God Bless America, period. I do have to think though, that if it had been Canada that had been attacked, there's no way in hell American stadiums would play the closest equivalent of either "God Save the Queen" or "The Maple Leaf Forever".