Silly girl. Such a tax would bring back the proposed coal export (aka the Gateway Pacific Terminal) terminal at Cherry Point WA, a short distance from the Canadian border.
 The construction of this new coal export terminal was blocked by the Obama administration, but no doubt Trump would approve it in a heartbeat.
i am sure the Americans would be happy to ship Canadian coal as well as their own, just as they ship Canadian propane through the nearby Ferndale, WA  terminal.