@Greengob

I am not sure what the process is at United Airlines when you buy a ticket from them but your flight is on Air Canada, or why they did not advise you of the eTA (and it's not a VISA). It is unfortunate that you were not advised of this by UA. However, it is listed on the Air Canada website.

For the benefit of anyone else who might read this thread...the AC website main page on the lower right in the "Read" section, has this link "Electronic Travel Authorization for Flights to Canada"

Click that link and you get this page

https://www.aircanada.com/ca/en/aco/...dates/eta.html

And this information is displayed



A number of people have provided you with the link to the Government of Canada website to apply for the eTA

It takes you to this page




You select "Apply online for an eTA"

And this page appears with the detailed instructions




And as others here have noted, you must apply in advance. You cannot do this at the airport.

Good luck and safe travels