When you put it this way, going to windsor would probably add Hamilton and London as well but then we'd be basically looking at an Ontario express line as 80% of it would be Ontario with Montreal at the end as a bonus 1hr
I do see how much of a tourist trap it could be to add a connection to the states (Windsor) but then on the other hand if you want to feel like you went somewhere different, you can't beat Old Quebec city and the fortress which feels like little Europe. But i'm truly biased.
EDIT) just thought about all the quality skiing i could get, hop on the train friday evening, ski sat and sun and come back without having to worry about being exhausted on the drive back!