I watched the Florida (delayed because the Leafs were playing at the same time), Leafs game in the pre-season. Saw him a good amount in London as well, he was clearly their best d-man last year.....but you always asked yourself it would translate to the NHL because of his size.
He looked good out there offensively and moving the puck. Plays a very simple and efficient game and gets the puck on net quickly with some zip. He's not a naturally good skater (I'm only saying this because some of the elite skaters can glide around at top speed)...but he's very competitive when he skates. His feet are moving non stop...that's where he's going to find success in the NHL. He's not a possession PMD but more of a good rushing PMD..which is great because that is something the Habs sorely lacked last year..mobility on their back-end.
He's done enough to make the team IMO (and also fits a huge need with his skating). I would be very surprised if he goes back to London without the 9 game stint, at minimum.