Permanent residents must have a valid permanent resident card (PR card) or permanent resident travel document (PRTD) to return to Canada by plane, train, bus or boat. Without one, you may not be able to board.
Your PR card needs to be valid when you show it. If your card expires, you will have to apply for a new one. You are still a permanent resident if your card expires.
When you become a permanent resident of Canada you are issued a PR Card that is valid for 5 years. To keep your permanent resident status, you must have been in Canada for at least 730 days during the last five years.