If you have COVID and get in a car and drive across you will still spread COVID "into Canadian communities". The plane is ancillary to the argument of either the test has value or it doesn't, and if it doesn't it should be gotten rid of.
Greyhound will be bringing busses across - should they have to bring a test as it would be very similar conditions (actually likely far worse if you've ever ridden one...) to a plane?
Not trying to be difficult, I'm just pointing out that being in a wheeled vehicle vs. an aeroplane is just semantics and has been brought up mostly by people wanting to drive across to shop.
Leaf's game with fully vaccinated people = safe. Plane with fully vaccinated people = unsafe.