score:5
Canadian passport only is best.
- one more thing to lose
Exactly. Replacing a lost or stolen passport is expensive and time consuming.
are there situations where it would be difficult for the american embassy to help me for example if I do not have my US passport with me ?
No. People show up at an embassy without a passport all the time. In fact, one the more frequent services of the embassy is to deal with lost or stolen passport. They may want to verify that you are a US citizen, but a simple photo of your passport should do the trick.
It's also not clear that the America embassy could do something that the Canadian couldn't.
I also have two passport and only take one wherever possible. In 100s of trips to 40+ countries I never had to deal with an unexpected event that required consulate or embassy assistance. These things are quite rare.