Upvote:6
The US ESTA website says explicitly:
citizens of Canada who are traveling with a Canadian passport do not need an ESTA. (emphasis mine)
I would deduce that without a Canadian passport you will need to go through ESTA.
I'm also a dual British/Canadian citizen, resident in Canada, and I found it well worthwhile to get a Canadian passport precisely to avoid this sort of thing at the US border. But I go to the US pretty frequently.