What documents does a permanent resident need to travel to Canada?

If you are a permanent resiident of Canada then you do not require an eTA to return to Canada but you must travel with your valid Permanent Resident Card or Permanent Resident Travel Document.
If you are not a permanent resident and do not have another type of visa for Canada then you may be eligible for an eTA (Electronic Travel Authorization) if you are from a visa-exempt country. The eTA is valid for five years and can be used for visits to Canada of up to six months. However, if your passport expires then your eTA will no longer be valid and you will need to apply for a new one with your new passport details.
People wishing to stay in Canada for longer than six months will require a different type of visa or may try to apply for permanent residency if they fit the criteria.