I went to the Port Roberts border in BC.
I drove up to the US border and told them I'm here to flag pole. I was asked do I have all the paperwork, which of course I did. Went into the US border building and got the paper that said I had left Canada. They didn't ask to see any of the PR stuff, but I took it in just in case. (Side note, had a laugh and a joke with them, which was a nice change.)
Drove round to the Canada side and when I pulled up the window I said I'm here to start my PR. The guy took my passport, looked at it and gave it back then told me to go inside and someone will see me.
Parked up and went inside and stood in line, there was only one person ahead of me. This guy waved me down to the end of the counter and I told him I'm here to start my PR and I handed over all the paperwork for him to see.
He had a quick look over it to check everything was OK (of course I checked it all as soon as I got it in the post box). The guy said, stay here and I'll be back. He went over to his desk and started doing something on the computer. Some of my details were out of date so confirmed my address (so my PR card would get to me) and also phone number. He then stapled the paperwork into my passport as a temp PR card and said if I travel I just show this until I get my PR card. He gave me some paperwork to read about starting life in Canada e.g. getting a new SIM card, needing to spend 2 years out of 5 in Canada etc.
After all that he put his hand out and we shook hands and he said 'Welcome to Canada'.
All in all took about 20 min in the Canadian border office.