Rust is covered for unlimited mileage in the US, I would be surprised if that was different up north. They do make a distinction between surface rust (not covered) and rust perforation (covered). It has to be rust coming from underneath paint or a rust hole in the car to be covered.
Aside from my rear fenders that are bubbling again, the other day I noticed a spot of rust (a bubble that has popped or whatever) on the roof of my car, on the front edge right where the windshield meets with the roof. I need to get to the dealership to have them look at it before I put my summer wheels/hood back on so my car can look sorta semi a little bit stock (unless they open the hood, then all bets are off haha.
The dealership I went to the first time my car was rusting (Modern Motors Mazda in CT, their service department is full of dickheads .. avoid at all costs) said they were going to void my warranty because they claimed the rust was caused by my wheels. The rust wasn't on my fender edge, it was at the seam between the rear bumper and the fender.. not really near the wheels.