Kaile Shilling, a writer and former theology student, says she moved from Los Angeles to Canada during the first Trump administration to escape America’s toxic politics. She never saw herself as the kind of person to hang a giant flag on the front of her house. But after Donald Trump was reelected last fall and started threatening to turn America’s famously polite and peaceful northern neighbor into the “51st state,” Shilling’s dual-citizenship husband unfurled an enormous red and white maple leaf banner on their home in Vancouver for all the world to see. “When he did it, I went, ‘F—...