Well, now the situation is clear, you PR card has expired and you have not met residency requirement. But you are still a PR. You can try to apply for PR travel document (
https://www.canada.ca/en/immigration-refugees-citizenship/services/new-immigrants/pr-travel-document.html) and most likely they will offer you to sign docs confirming that you understand that you have not met residency requirement and voluntary renounce your PR status. Alternatively you can try to come to Canada by land using your expired PR and COPR and the officer at the border will initiate a case for you and it will go to a judge and if you keep your PR staus or not will depend on the judge's decision. (Both scenarios happened to my friend: she tried to apply for a travel doc, was offered to renounce her PR and get a visitor visa instead, she denied. Came to Canada by vehicle (from US), attended hearing and was able to persuade the judge that she had valid reasons to be out of Canada, got new PR card)
If you lose your PR, then...sponsorship. You'll need to provide very detailed information regarding your relationship, probably what caused the separation, if you were in contact during these years (you probably had to communicate one way or the other as you have a child together), what you did to re-establish your relationship (councelling, correspondence, visits etc). It is hard to say how you can prove your reconciliation, each situation is unique, I'd say tell them truth and nothing but the truth
