Canada's entry rules are changing, starting March 15, 2016. Citizens from visa-free countries will need to obtain an Electronic Travel Authorization (eTA) before flying to or transiting through Canada. Exceptions include U.S. citizens.
Requirements for flying or transiting through Canada
Most visitors flying to or transiting through Canada will need either a valid visa or an Electronic Travel Authorization (eTA). In order to fly to or transit through Canada without a visa, you must meet the following requirements:
Electronic Travel Authorization (eTA)
Travellers will need an eTA before they can board their flight to Canada. You are encouraged to appply for an eTA before you book your flight. It costs CAD 7 to apply. An eTA is valid for up to five years and allow repeated entries into Canada provided your passport does not expire during this period.