It's simple. If sued in Canada, refuse to pay and cease operations. Tell them to go f%$k themselves.
Unfortunately, it's not that simple. First, they can seize whatever assets they have in Canada. Second, a Canadian judgment can be taken to the US and enforced against their assets here. That's why I say they should leave Canada now. The due process clause precludes enforcement of a judgment which was obtained without "minimum contacts." If they aren't doing business in Canada, and they don't have property there, then there is no "minimum contacts."