Hard to interpret this sentence, are you suggesting cut and cover? The train is 35 metres below ground at the Airport so that doesn’t exactly save you any money/effort.
I was suggesting elevated, though cut-and-cover likely isn't too problematic, because there won't be much in the way of the usual services.
Wow that's deep. Is there a map showing where the station actually is? A crappy one I see on line, has the tail tracks heading due map south (perpendicular to the 20), ending half-way under the parking structure (which look triple the size last time I parked there - I normally taxi, or take the train). Are you saying the tail tracks under the parking structure are level, and don't start rising up?
Which only leaves about 900 metres to the current intermodal station at Dorval, and about 75 metres to the south end of the parking structure.
Which might preclude elevated - at least until they want to get over the railway tracks and Cardinal Avenue. What's the maximum incline for the REM and the Alstom Metropolis? Presumably at least the 8% the Flexity can handle (I'm not sure what the Flexity limit is either, other than the existing 8%). Which would take over 400 metres to get to a portal if the track is 35 metres deep!
That station sounds unusually overdesigned compared to all the other new stations. I wonder what drove it so deep; I don't think the 13 is that deep under the runways. Is there a nuclear fallout shelter under the terminal of something, when they first built it in the 1950s?
Hmm, is this the station excavation under MPETIA (!

) parking structure? It does look deep on
Google Maps: