https://en.wikipedia.org/wiki/Category:Volcanoes_of_the_Rocky_Mountains

https://en.wikipedia.org/wiki/Geology_of_the_Rocky_Mountains#Terranes_and_subduction

There currently aren't any active volcanoes in the Canadian Rockies, but there is still magma towards the base of them that we'd run into if we tried to bore tunnels straight through. In theory, we could bore tunnels at a sharp incline to go over the magma; but that basically eliminates all the benefit vs just building rail lines on the surface like we already have, plus there's the added complexity of trying to make an earthquake-safe tunnel that crosses a fault line.