The long YUL delay till summer 2020 might be influenced by likely low numbers for the winter period to Montreal. I think YUL service was due to start in August but if the delay in delivery for this route means it even arriving in December/January maybe better to start it up once high season kicks in again even if they had the aircraft ready to go beforehand. So if that was the case then you might see greater use on winter sun destinations. Or it is a genuine 6+ month delay on some of the aircraft scheduled in. Hard to know exactly.