http://www.cic.gc.ca/english/information/faq/pr-card/pr-card-faq12.asp
No matter how you travel back to Canada, all permanent residents entering Canada must satisfy the border services officer that they have valid permanent resident status. A valid permanent resident card is the best proof of your status.
If you do not present your card when you return to Canada, you may be asked to show one of the following documents:
* a completed Confirmation of Permanent Residence form;
* the original Record of Landing (if it is dated 1973 or later);
* a passport stamped with the date you were granted permanent residence (if your Record of Landing is dated 1972 or earlier);
* a certified true copy of a Record of Landing document issued by CIC National Headquarters; or
* a letter issued by CIC National Headquarters attesting to your permanent resident status.
The border services officer may also need to confirm your permanent resident status by asking you questions and checking our information systems.
That should answer your question.
BUT
http://www.cic.gc.ca/english/information/faq/pr-card/pr-card-faq11.asp
The card gives holders reliable proof of their permanent residence status in Canada. The high-tech security features make the card extremely resistant to tampering or duplication. The
card simplifies document screening for transportation officials because all permanent residents must produce the card when boarding a commercial carrier to Canada.
I am from a non-visa exempt country, but I will go with my husband to US sometime this year and will just do what is required of me. Based on their website, car travel is the best option if no pr card yet. Because you can just present the following documents in the border control. By plane, airport people will ask for your card.
