BRUSSELS — As President Donald Trump upends U.S. foreign policy, negotiating closer relations with Russia, threatening NATO allies and pausing cooperation with Ukraine, Washington’s traditional partners — and best customers — are rethinking their dependence on American weapons systems. From Canada to Europe, calls are growing to steer future defense spending away from U.S. equipment and toward their own industries, even as many concede there is no quick fix after decades of dependence. The U.S. pause of intelligence-sharing with Ukraine this month, and Trump’s threats to annex Canada and Greenland, have laid bare the risks of counting on the United...