ExXB:
Interesting new scheme, which I had not kept up on. It seems there is an exception for those dual citizens using a US passport. But the wording is so vague that I'm sure there will be screw-ups.
From Gouvernement du Canada website:
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 enter Canada if you are travelling with a valid U.S. passport.