I went flag poling yesterday in Pt Roberts, WA.
I drove across the border (to get cheap gas and pick up a package). I did not tell the US border person I was going to get my PR on the way back (mistake! because as you guys have been talking about one needs a piece of paper to prove that you were in the US... however it turned out not to be a problem because the border people were just super nice).
Crossing back into Canada, the guy told me that I usually need that paper, but that it's ok and they won't send me back and forth, so I should just come inside.
The thing with Point Roberts though is that since it is a Peninsula there is no other way crossing the border and getting into the US other than that one border. So, he knew that I crossed it for sure...
An officer inside took care of my case. She told me to double-check all the information on the CPR and then told me to wait. She typed some information into her computer for a while and then asked me only if I have ever been charged with crime, I said no and she had me put my intials and sign two print outs and went through the next steps with me with an information sheet for new PRs.
Everybody was really nice and it took about 10min with waiting etc.
I will get my PR card in about 4 weeks via mail and currently have my CPR stapled in my passport. My student visa was taken out. I'm gonna have to get a new SIN when I have my card.
I recommend going to Point Roberts for flag poling if you live close to Point Roberts. You can do it by foot or car.