The standard rule for all permanent residents is as follows:
in order to maintain your permanent resident status in Canada, you must reside in Canada for 720 days in every 5 year period. These 720 days do not have to be immediately following landing. Exceptions to this rule include:

1. If you are accompanying a Canadian Citizen spouse abroad
2. If you are employed by a Canadian company abroad
3. In very limited circumstances humanitarian and compassionate reasons are also taken into account

Six to eight weeks after landing in Canada, your Permanent Resident card should be mailed to you at your address in Canada. If you do leave Canada after landing without first obtaining a Permanent Resident card, you must apply at a Canadian Embassy or High Commission for a ?Travel Document for Permanent Residents? prior to returning to Canada.