Electronic Travel Authorization (eTA) is required for visa-exempt foreign nationals travelling to or via Canada by air. US citizens and travellers with a valid visa are exempt.
To enter Canada, you must have applied for an eTA (Electronic Travel Authorisation) no later than 72 hours before your departure. If you are travelling without an eTA authorisation, you may be denied entry to Canada upon arrival.
To apply for an eTA, you must have a valid passport. You must bring the same passport when travelling as the one you used for your eTA application.
The eTA is valid for up to 5 years or until your passport expires, whichever comes first.
Remember it is your own responsibility to apply for and get your eTA approved.