We just did this for my in-laws last Saturday. Detail like this:
The closest port of entry for people from Ottawa region:
Prescott/Ogdensburg.
The driving distance is about 100km from downtown to the Prescott-Ogdensburg bridge (HWY417 -> HWY416 -> HWY16).
Here is the list of documents that I have bought with me:
Passport
Confirmation of Permanent Residence Letter (landing paper)
Basically what you need to do is driving across the bridge to get a refusal letter from US custom office. Then just drive back to Canadian side hand over all documents simple as that.
Before, there is a small fee for each bridge crossing. ($3CAD or $2.75USD per crossing). But we did not pay any fees I guess because that the bridge is doing maintenance right now.
When you arrived at US side, tell the officer that you are here for flag-poling and they will take the passport and landing paper from you, ask you to park aside and get in the building for some paper works. This should takes less than 20minutes assuming nobody was ahead of you and no line up.
After you obtain the refusal letter from US custom office and drive back to Canadian side, you should tell the officer that you are here for landing. They will ask you some basic questions about whether you bought anything from the duty free store or is there any other people with you for this trip and etc... After that you will need to park near the building and enter for further landing process.
The officer asked whether you had committed to any crime, any change to family members, any goods to follow. And then, just handed over all documents to her. She asked me to wait a bit and went into her officer for some computer inputs. After it's done, she told me congratulation and remind me to update my health card and SIN card. This should only takes about 20minutes if you are the only one there. She also mentioned that the PR card will mail to the address within 4-6 weeks ( do not need take ID photo there, she scanned the one on the landing paper).
Officers from both side were pretty gentle from my point of view. You shouldn't run into any issue as long as you know what you are doing there. Good luck.