Air Canada refund the money if you are instructed to move out of a preferred seat that you paid for, but you do have to chase them for it.

Most of the time I see people asked to move, it is very much 'ask' not 'instruct', and it is to accommodate people who want to sit together, so I don't have an issue pointing out that I selected a specific seat, and paid for it for a reason. If there is an aircraft change, or other real reason then that is of course different.