Canada has entered into Social Security Agreements with over 50 countries. These agreements allow late-arriving immigrants to "totalize" periods of contribution from their home country to meet the minimum residency requirements for Canadian benefits.
For example, to qualify for OAS while living outside Canada, a 20-year residency is normally required. Under a totalization agreement, 10 years in Canada and 10 years in a partner country may satisfy this technical requirement, though the actual payment remains prorated.
This system prevents the loss of pension credits earned abroad and ensures that the transition to the Canada Pension System does not result in a complete reset of retirement eligibility.