New Canadian Entry Rules.

Starting November 10, 2016, all air travelers will need to have certain documents to travel to Canada before they can board their flight. American citizens will have to have a passport and meet the basic requirements to enter Canada.
Canadians, including dual citizens, will need to show proof they are Canadian citizens through a Canadian passport or other appropriate documents to fly to Canada. However, American-Canadian dual citizens do not need a Canadian visa or to show proof of Canadian citizenship if traveling with a valid U.S. passport.