Thanks I’m gonna ask to cicA COPR that has been 'stamped' at border is more than a landing document - it is proof of PR status. (It is not before that though).
That said, I do not know well enough to say how this works - esp right now - for inland applications, nor whether COPR (stamped) can be used for the purpose of starting a sponsorship application.
I would think that a stamped COPR and UCI number therein (which will be the PR card number) would be sufficient to start a sponsorship app, but don't know.