A commercial approach on such new operations by semi-charter companies is to put the nonstops on sale (in this case from both Montreal and Quebec) on a given day of the week, and a limit of say half a planeload each for bookings. Knowing how the typical demand curve goes for bookings over time, you get to a point say four months beforehand, or as the 50% point comes close, and reassess whether to consolidate into one flight with a stop, or run the two separate ones, maybe consolidated for part of the season only. I'm sure TSC have their own way of doing it.
UK IT operators to the Mediterranean used to be experts at doing this.