Electronic Travel Authorization
Starting March 15, 2016, visa-exempt foreign nationals who fly to or transit through Canada will need an Electronic Travel Authorization (eTA).
An eTA is a new entry requirement for visa-exempt foreign nationals travelling to Canada by air. The authorization is electronically linked to your passport and is valid for five years or until your passport expires, whichever comes first.
If you are a U.S. Citizen or you have a Temporary Resident Visa in your passport you do not need an eTA