In theory, the layout of a parking garage can be modified to allow a protected covered/decorated pedestrian 'tunnel' throughfare that doesn't even have a view of the garage except through some windows -- and a couple sets of access doors -- while still keeping most of a parking garage floor for cars.
What type of parking garage is it? I am not familiar with this particular one. The areas that cars can drive through and the parking space layout may have to be changed, depending on how the parking garage is designed (e.g. just pillars that permits a parking spaces layout redesign -- swapping where cars drove through versus parking spaces -- or a lot of immovable load-bearing concrete walls). Certain parking garages have flat levels with just a grid of pillars, and in theory, you can just redesign where the cars drove/where the cars parked, allowing mitigation of loss of parking spaces. Most below-ground parking garages aren't designed this way, though.
The question is -- how many parking spaces would be lost in a 'pedestrian tunnel' scenario? With GO RER electrification, may divert enough cars from that particular building to allow such spaces to be sold off to Metrolinx. It might be surprisingly few, or might be devastatingly huge.
At the Aldershot south parking lot, I was intrigued how Metrolinx added 50 parking spaces during their first stage of incremental parking lot extension (out of two done recently) simply by initially changing the layout of the south parking lot, shifting where the cars drove through, to allow parking spaces at the very southern edge rather than driving lane flush against the southern curb. So the layout efficiency rearrangement meant more surface-area of parking spaces got added than asphalt surface-area.
