Could there be an upside to Trump's unhinged attacks on Canada?

Donald Trump is rather obviously the worst thing to happen to Canada since, well, the last time Americans tried to invade. But another possibility is brewing, if in a quiet, careful, Canuckian way: that he could also be one of the best. Trump's threats towards Canada appear delusional. But it's useless to ask if his remarks about the "51st state" are a joke. He doesn't joke about things he doesn't want, and the jokes are designed to soften the ground. He says Canada is freeloading militarily (because the two countries both defend the Arctic). He says the US is subsidising…