I think I misunderstood the OP's question. I was thinking about situation with 2 citizenships (US + 1) and Canadian PR.
When tickets are booked, you need to write your name exactly as it is written in the document you'll be using while travelling (passport) and country which issued the document (passport).
So when there is just one citizenship (US), the situation is even easier.
The objective of the of the air company is to determine before boarding that you'll be allowed to enter the country you are flying to and the company will not have to fly you back and pay fines if you are denied entry (yes, air companies are fined if they bring passengers without proper docs). So have your passport and PR card ready just in case.
When you are in Canada, you'll need just your PR card (if you are using the scanner), officers might ask for both passport and PR card (personal experience)