As Canada deepens ties with Europe, could it leave U.S. banks and dollars behind?

Prime Minister Mark Carney last week pointed to international payments as a system that "can be used as leverage against you" before telling the EU that he sees this as an area for "deep co-operation." Why are countries increasingly worried about the leverage the U.S. has over their financial systems, and what would Canada have to do to protect itself from American rogue behaviour?