All foreign nationals from visa-exempt countries travelling to or transit through Canada by air must first obtain an Electronic Travel Authorization (eTA). This eTA is valid for up to 5 years. Canadian citizens, including dual citizens and Canadian Permanent Residents, cannot apply for an eTA. People who have an expired PR card or one that is expiring within the 9 months, should apply for a new PR card as soon as possible to avoid issues with travel plans. 

American citizens are exempt from the eTA program, but U.S. Green Card holders are not.

 Find out if you need an Electronic Travel Authorization (eTA) or a visitor visa