WASHINGTON — Canada has filed a sweeping trade case against the United States at the World Trade Organization, lobbing a diplomatic grenade at the Trump administration’s “America First” approach amid an increasingly embattled trade relationship between the longstanding North American allies. …The case could expand into a multinational trade dispute given that Canada, a champion of global agreements, filed it in a way that allows other countries to join. …“You can equate it to a gold medal hockey game: Canada and the United States are playing, but all of the referees are from the U.S.,” said Andrea van Vugt, vice president for North American affairs at the Business Council of Canada, a group representing about 150 companies. “The Canadian government really has no choice but to stand up for Canadian industries on this.”