It's funny, but there actually is a pre-existing tunnel under the CPR tracks very close to this location that could be repurposed quite easily.
It's known in the local graffiti scene as "Cow Tunnel." From what I can determine, this is a left over passage from way back when this area was farmland. Likely built to allow cattle grazing and movement on both sides of the CPR embankment.
I really enjoy this little secret spot and it would be a bit of a bummer to see it developed, but oh well lol
Edit: after looking more closely at the Draft Plan, they actually noted the "existing agricultural underpass" and looks like it will be lining up with parks in the proposal. Neat.