[Nouvellecosse]

Both. The distance is quite wide, and there are a couple islands that would allow part of the crossing to be bridge while part would be tunnel.

 

[Nouvellecosse]

you mean like L-H Lafontaine bridge/tunnel? Is it cheaper?

Underwater tunnels are always more expensive than bridges, but having a shorter tunnel section augmented by a bridge would certainly be cheaper than a tunnel for the full width.