I did some googling. Here is what I came up with - a 2012 Conference Paper.
http://webcache.googleusercontent.c...3365b1f226b6db8084a+&cd=2&hl=en&ct=clnk&gl=ca
Measuring that the Gardiner is about 32m wide in this area, it appears that the entire water treatment facility is about 50 across. Lets say we need a 60m span to get across it. If an alignment closer to the railway is chosen, the existing Gardiner would probably be removed just west (about 100m) of Cherry - at the expansion joint.
The current Gardiner in this area has spans of about 20m. This was built in the 1950's. At the time, the steel strength was 230 MPa, while now it is 350 MPa (or 485 MPa is High Performance Steel is used - although not common in Canada). Also, when built, prestressed concrete was in its infancy so there was not confidence to have large spans. If built now, the cheapest alternative would probably be 2400mm deep NU (Nebraska University - a more efficient concrete shape for higher strength concrete than the previous AASHTO or CPCI girders) Girders with a span of about 50m. To get a get longer span, a +/-20m segment could be put above the pier, with a 40m drop in span, with the girders post-tensioned. Alternatively, steel girders can easily be built with end spans of 60 to 80m and interior spans up to 120m. Finally, the existing Gardiner in this area has expansion joints at about 100m spacing, whereas now with modular joints, they span easily be 500m apart - if not more.
Another image form that paper shows the height of the treatment facility. It is about 7.5m above the ground elevation. I am not sure, but it looks like the bridge deck is about 10 to 12m above the lakeshore - so if the concrete bridge of 2400mm depth, or the steel girder of 2000mm is used, there would be adequate clearance to pass above it.
So the conclusion is that if this sketch is anything close to being accurate, there would be no problem at all in spanning the facility.