If you have a US Visa and are re-entering Canada by car from the US, you can use your passport and signed COPR to get into Canada. However, if you're entering Canada through an airport, unless you applied for a PR Travel Document (PRTD) in your home country, you will not be able to get back into Canada without your PR Card.
The COPR is NOT a travel document (and this is clearly stated as such on the COPR). You cannot rely on it for travel except, for some weird reason, when crossing the US border in a private vehicle (but not in public transportation, e.g. bus or train).
Also, PR is not 'printed' in your passport after you get it back once you receive PPR - the thing that is printed in your passport is your PR visa, which is a one-time entry visa that allows you to enter Canada, for one time only, in order to claim your PR. It is not evidence of your PR.
Even with your PPR email, your COPR letter, and your PR visa stamp in your passport, you are not truly a Permanent Resident until you land, the immigration officer makes you sign your COPR in front of them, and then they say to you that you are officially a permanent resident. Your PR Card is the only official evidence of this PR, not the other 3 documents (i.e. PPR email, COPR, one-time entry PR Visa stamp)
So, to sum it up:
- Leave Canada WITH PR Card, come back to Canada via any means: bring passport and PR Card and they will let you back in
- Leave Canada WITHOUT PR Card, come back to Canada via US border in PRIVATE vehicle: bring passport and signed COPR, and they will let you back in
- Leave Canada WITHOUT PR Card, come back to Canada via airport/public transportation: get PRTD from home country; bring PRTD and passport, and they will let you back in
- Leave Canada WITHOUT PR Card, come back to Canada via airport/public transportation WITHOUT PRTD: they won't let you in