Closing the loop on this, I'm just going to book a flight for my soon any myself and my wife can fend for herself when she knows her schedule for sure

One interesting thing I've learned looking into this - which perhaps is common knowledge - is that when you cancel an Aeroplan ticket the seat doesn't automatically return to their inventory. If the flight is oversold (which I know this one will be), it will not return to Aeroplan's inventory. So the plan to cancel my wife's ticket and immediately rebook in my son's name would have ended badly had I attempted it!