My thoughts are similar to yours. The Competition Bureau may not like it, but a TRU acquisition may be the only hope for the Mastermind chain.
I also agree that they might stipulate maintaining the two brands separately, which TRU might not mind. I could see Mastermind carrying on as the educational toys and game brand within the larger TRU universe.
In Moncton, Mastermind has the advantage of being on the other side of town from TRU. This could give them some protective advantage.