This is a reminder that in effect as of November 10, 2016, visa-exempt foreign nationals must obtain an eTA before boarding a flight to Canada – This includes Transiting passengers through Canada as well.
The Government of Canada's official website to apply for an eTA. It only costs $7 CAD. Most eTA applications are approved within minutes of applying.
New entry requirement now in effect: visa-exempt foreign nationals who fly to or transit through Canada need an Electronic Travel Authorization (eTA). include U.S. citizens and travellers with a valid Canadian visa. Canadian citizens, including dual citizens, and Canadian permanent residents cannot apply for an eTA.
Entry requirements for other methods of travel (land, sea) have not changed.
Find out if you need an eTA http://www.cic.gc.ca/english/visit/visas.asp
Find out if you need an eTA, how to apply and what other documents you will need to come to Canada