You don't need to actually cross the border if you don't want to. You can:
1. just go to the US side of the border, tell them you are landing as Canadian PR
2. they will send you to their secondary check, where they give you a paper
3. then you go to Canadian side, say you are landing
4. give them the paper, passport and CoPR
5. they ask you a few questions, tell you to sit and wait, and call you in like 5-10 mins and tell you it's done.
If you actually want to enter US, make sure you can (visa exempt passport or passport with a visa), and on the way back to Canada say again that you are landing (take steps 3-5).
I did the first way (called flag poling), there were no problems.