WASHINGTON — Born in Canada to an American mother, Ted Cruz became an instant U.S. citizen. But under Canadian law, he also became a citizen of that country the moment he was born. Unless the Texas Republican senator formally renounces that citizenship, he will remain a citizen of both countries, legal experts say. That means he could assert the right to vote in Canada or even run for Parliament. On a lunch break from the U.S. Senate, he could head to the nearby embassy — the one flying a bright red maple leaf flag — pull out his Calgary, Alberta,...