OTTAWA — The video playing was clearly Pete Hoekstra, the frequently combative U.S. ambassador to Canada. But something was off. He kept referring to Canada as a partner? “For all of the critical things that we need, Canada would be an ideal partner,” Hoekstra said in a prerecorded conversation at a conservative think tank in March. Hoekstra ticked off the ways the two countries could work together: deepened military cooperation in the Arctic, including through Trump’s “Golden Dome”; beefed-up energy cooperation on oil and gas, critical minerals and uranium; coordinating on artificial intelligence. At one point, he even cited the...