I am a dual citizen of the U.S. and another country. Do I need an eTA?
No. As long as you travel with a valid U.S. passport, you do not need an eTA to enter Canada.
American citizens, including American-Canadian citizens, must carry proper identification and meet the basic requirements to enter Canada. You do not need a Canadian passport, a Canadian visa or an eTA to fly to Canada if you are travelling with a valid U.S. passport.