Canada Has New eTA Requirements
Canadian government recently has announced new regulations about the Electronic Travel Authorization (eTA). The changes which are already in effect require all foreign nationals who travel to or transit through to have eTA visa. Holders of US passport and valid Canadian visa are not obliged to have eTA. Canadian citizens and dual citizens are not required as well.
The eTA is valid for 5 years or until the passport expires. If you have a new passport you need to apply for new eTA. Being on eTA, the holder can visit and stay in Canada for up to six months per visit.
More information about eTA you can find here.