They'll fill out your COPR and let you sign it and have you keep it. You would need your COPR to apply for a SIN, open a bank account, apply for health insurance, driver's license, etc. It would be your proof of being a PR while you still don't have your PR card.
Regarding going out and back without a PR card and just a COPR, I think it's possible, I'm just not sure how much of a hassle it would be, since the airport (Toronto Pearson) has only 2 entry lanes: "PR Card holders/Citizens" and "Visitors/Non-PR Card holders."
I got my PR card after about 8-9 weeks of landing