Mostly Canadian, bust also Fin, Slovak, Czek, German.. and.. I may have missed some. Heck, I don’t even think most American college teams are 100% American as many Canadian kids come down on scholarships.
It is no different than any other professional sport. They recruit from around the world. I have a friend who played 25 years ago for the Swedish National Junior team. He was not quite good enough to make the Olympic team. He still got a full scholrship to the University of Maine to play hockey. He was not good enough to go pro. He went to work for a lumber mill in Maine.
His son MAY be good enough to go pro.