@CanadaGirl30 :
Hi, being from a country (France) that only needs eTA to travel to Canada, I only had to send photocopies of my passport (and my partner's) main page and those with stamps, as well as officials photos (went to London Drugs here in Vancouver), and a completed and signed document they send in the email body (which is a pain to complete and print, I ended up modifying the HTML code from the gmail page to complete my info, and selected the lignes to print).
Then you have to send all that in a tracked envelope, in which you have to also include another tracking envelope for them to return the COPR (confirmation of permanent residency) letter.
(The following is my understanding since I'm not there yet)
Once you get the return letter, for my case (somebody already living in Canada and close to the border), you go at the border with this letter, your passport, and I guess as much documentation as you can just in case, do a flag pole, possibly without entering the US or even talking to a US officer (or you could spend the day in the US to visit if that's your thing).
There no need to leave the country for any particular amount of time.
I'm currently waiting for the return envelope to depart from Ottawa. I know that my letter reached them last Thursday.
PPR is indeed the golden email.