I know it's been done. There wouldn't be any logical reason to prevent it since the Canadian version has a few supposed 'safety upgrades' over the U.S. version as I recall (such as a beefier rear bumper, I believe).
In fact, the NEW 2nd generation Ford GTs are all made in Canada and shipped down to buyers in the States.
You'd have to check with U.S. Customs for the latest 'red tape'. Bureaucrats with seemingly nothing better to do are constantly tinkering with that sort of thing.