There are pros and cons to off-road bike paths. One major con is that they are mostly shared-use, so there are potential conflicts. But they are largely free of car/bike conflicts, and there are few lights and no needless stop signs to frustrate the cyclist. Another con is that they are away from commuter routes, yet some come close to potential trip generators like York University.
Paths don't have to be shared use, it's just that the city tends to cheap out and not build a sidewalk, forcing pedestrians onto the path. We do have some bike-only paths in Toronto, such as the ones on Lakeshore East (north side only) and Eglinton West.
Paths do not eliminate car-bike collisions, they just concentrate them at intersections. Properly designed bike paths migitate this risk, but I am not aware of many well-designed bike paths in Canada. Whoever designs Canadian bike paths does not seem aware that cyclists are not simply pedestrians with wheels, that they require a different crossing design than a crosswalk.
For example, the new segment of the Martin Goodman Trail across the top of Ontario Place has terribly designed intersections. These
two articles explain some of the issues of the design. The main issues are that priority is unclear, cyclists and pedestrians are not realistically separated (painting a bike symbol on half the crosswalk will not make cyclists go there), and visibility is poor.
The Railpath is perfect as it is entirely grade separated, but is of limited utility as it is so short - it should at least go to Dufferin and Queen, but ideally Strachan/Wellington for a downtown route. What I'd like to see is the completion of the proposed CN Newmarket sub path between Downsview Park and the Railpath; that would provide a flat north-south route through really hilly terrain. Another one I would love to see is one on the unused spur track lands along the CP North Toronto Sub, especially between Osler (connecting to that Railpath) and Yonge, if not all the way to the Don River. Voila - a bike expressway.
I think the biggest issue with the Railpath is that some of the interchanges are awkward. For example, the path just ends at the sidewalk on the corner of Dundas and Sterling. How are cyclists riding along Dundas supposed to use that entrance? The only legal way is to dismount, cross the street if necessary, and walk along the sidewalk: hardly a practical or desirable option. The design has completely ignored cyclists, as is common in "mixed use" trails in the city.
If we want to encourage cycling, we need to build bike paths that are not unusable by cyclists. The south entrance to the Railpath should be very popular because it is the end of the path and "connects" to a popular cycling street, yet its design strongly discourages cycling.
The main issue is that it is very awkward to leave the Railpath and travel east. To facilitate this manoeuvre, the path should be extended south under the bridge and onto the driveway of that industrial thing on the south side of the street. From there, cyclists just have to make a right turn into the bike lane.