No idea on comfort, but if the bus segment has a KL flight number (I think it does) then don't forget to claim your miles for the bus segments. You'll probably need to send your tickets in for a manual credit (that's what I have to do for the KL train service to Antwerp).
You should call KLM's Canada service desk (or whoever operate as KL agents in Canada (NW?)) and ask about the suitability of this bus service for babies.