Effective March 2016, the Government of Canada (IRCC) requires that anyone traveling through Canada must apply for an Electronic Travel Authorization (eTA) to fly or transit through a Canadian airport; which costs $7 CAD. According to IRCC, most people need a Visa or an Electronic Travel Authorization to travel to Canada; some may only need a valid passport. The only exceptions to needing an eTA are U.S. citizens who can show proper identification at the border.
Canadian dual nationals must travel with a valid Canadian passport. If their plane leaves within 10 days, they must apply for a special eTA to travel with their passport from a visa-exempt country.