WASHINGTON — Fixated as we Americans are on Canada’s three most attention-getting exports — polar vortexes, Alberta clippers and the antics of Toronto’s addled mayor — we’ve somewhat overlooked a major feature of Canada’s current relations with the United States: extreme annoyance. Last week, speaking to the U.S. Chamber of Commerce, Canada’s foreign minister calmly but pointedly complained that the U.S. owes Canada a response on the Keystone XL pipeline. “We can’t continue in this state of limbo,” he sort of complained, in what for a placid, imperturbable Canadian passes for an explosion of volcanic rage.