Hello fellow Canadian! I almost never book via AC, but this is what I would attempt: I would try opening a fresh browser window on a computer and manually setting the region to Canada (if it didn’t already do it automatically) and trying the upgrade using the PNR search from there, instead of via the app.

Years and years ago, it used to be a workaround for ZIP code validation by taking the three numbers from your postal code and adding two zeros. For example, H2Y 1S6 would become 21600. For the state, use whatever state has ones starting with 21, or just use Alaska. I don’t think state used to be as critical as zip code. This probably doesn’t work anymore, but thought I’d share what I used to do just in case it does.