If by a few weeks time you mean something around 24-30 January then I would guess your flight from YUL to Boston is cancelled and/or a mis connect as nothing arrives into YUL from Paris before 1400hrs and the single daily YUL - Boston is at 1345hrs.
Are you sure about that?
This is what I see.
4 flights a day... were they just cancelled? It's also the same on the AC website....