Canada Entry Rules are changing
New entry requirement now in effect: visa-exempt foreign nationals who fly to or transit through Canada are expected to have an Electronic Travel Authorization (eTA). Exceptions include U.S. citizens and travellers with a valid Canadian visa.
Until September 29, 2016, travellers who do not have an eTA can board their flight, as long as they have appropriate travel documents, such as a valid passport.
More info : http://www.cic.gc.ca/