The eTA for transits in Canada
You still need an eTA even if you are only making a transit in Canada and continue onward to your final destination. It does not matter if you are staying at the airport during the stopover period. There is no special eTA for a transit or transfer, you can submit a regular Canada eTA application through the eTA form.
Transit through Canada
Many travellers fly through Canada to the United States or Mexico. It is important to apply for all the required travel documents before starting your trip. If you are flying through Canada to the USA, you need both an ESTA as well as an eTA. The ESTA is the travel authorisation you need for your trip to the United States. The eTA is the authorisation you need for your flight to Canada, even if you are not leaving the plane.
Exception for tanking
There is one exception where the traveller does not need an eTA when landing in Canada. This applies to planes that are only stopping in Canada to refuel before travelling onward. Travellers are not allowed to leave the plane during the stop in Canada. If they are travelling to the United States, they also still need an ESTA. In other words, this concerns a stop in Canada, but not a transfer to another plane.
eTA Canada for transits
If you are on transit through Canada, you can apply for this travel authorisation. The costs for this are £19,95 per eTA. The eTA is processed right away and is generally granted the same day. Take note: you already need this permit before checking in your bags for your flight to Canada. It can take up to 72 hours before an applied for eTA is granted, meaning it is wise to apply for one right after you have decided you are flying to Canada. It is not necessary to have already booked flight tickets at the moment of applying. You also do not need to have an exact date of departure, the eTA is valid for five years.