Adam Smith

You're caught between the AC tariff, which references Canada's largely useless APPR and should, in theory, enable you to book what you're looking for ("must rebook you on the next available flight operated by them, or an airline with which they have a commercial agreement, on any reasonable route from the same airport" - see the second post of this thread for more) and AC's internal schedule change policy, used by its staff and travel agents, which basically says they should keep you on AC metal as much as possible.

So, to answer your question, can they? Absolutely. But will they? Hard to say. You will likely need to find a sympathetic agent and have them escalate it to a supervisor to get clearance to do so. This may require HUCA and a willingness to cite the tariff/APPR - i.e. show them you know your rights.

But a key challenge here is that it turns on the word "reasonable". APPR doesn't have a quantitative threshold you can cite to conclusively prove that AC's proposed itinerary is not "reasonable" but yours is.

The one quantitative threshold you do have in your favour is a more than 3 hour change in departure or arrival time, which is grounds for a refund under AC's own policy. If you can re-book with another carrier for a price you're happy with, you may want to consider having AC refund you and re-booking.

If you pay the (undoubtedly huge) fare difference, maybe. Otherwise, definitely not.