In the heart of the City, I don't see this happening in the foreseeable future.
I think the Gardiner west of the Humber could spare a lane fairly easily and there is some room in the ROW in spots as well.
That said, it is key to set up some time of reserved/preferred lanes right around the bus terminal to get buses to/from the Gardiner.
Beyond that, I think, if they get rail service up to promised/planned levels, it should do a lot to dissipate the traffic. (Service that is every 15M or better on the core of the K-W and LSW lines, and every 30M or better on Milton will draw people out of their cars.