LauraJean, last year when the New York Islanders fans booed the Canadian national anthem, not once but twice AND burned the Canadian flag in the parking lot, do you think Canadians quit going to New York because they thought that all New Yorkers were like that? I don't think so.
How about when the US Ladies hockey team had the Canadian flag on the floor of their dressing room during the last Olympics? Did we boycott the US because of that?
Perhaps you could explain to your son how some Americans also treat other countries' anthems and flags with disrespect and that it doesn't mean that all Americans or all Canadians are rude and disrespectful.
Montreal is a beautiful city with wonderful people and it would be a shame if your son loses the opportunity to experience that, let alone miss his hockey tournament.