Just thought I'd share my flag poling experience with you guys:
I flag poled at saint-bernard de Lacolle on the 6th of March and became an official PR!, and in case you were wondering, you do not need a US Visa to do this.
However, I was asked to pull over for further questioning (maybe it's only because I have a Lebanese passport). The officer who did the questioning was very polite, and the questions were very standard (when did you come to Canada, where did you study, where do you work, when was the last time you came to the US, where did you travel to the last 5 years..........). the whole thing was over in like 20 minutes. After that they hand you a paper that you need to take to the Canadian side (CBSA).
After the questioning is done on the American side, they tell you where to do the U-turn and then you head back to Canada. In the CBSA building, everything went very smoothly. The entire thing was done in 15 minutes. They ask for your COPR and your CSQ and your proof of Status in Canada (Work permit, study permit). And they ask how much money you have available to you for the next 3 months, so it might be useful if you take a bank statement with you. After the processing is done they congratulate on becoming a PR and then you're on your way.
Everyone I encountered (American officers, Canadian officers) were very polite and courteous and the entire flag poling experience (including the driving to and from) lasted around 2 hours only. So I would definitely recommend it.
Best of luck to everyone.