Ummm, there are about 24km of Waterfront Trail (paved multi-use path) on a straight-line basis there are about 41km of shoreline, but if you actually weave in/out its closer to 113km.
So I don't think its fair to say the majority of Toronto's waterfront is 'trails'.
We know this, because
@Metroscapes was kind enough to do the work for us:
An analysis of Toronto’s shoreline, breaking down it’s length, ownership and public access.
metroscapes.ca
Note that there are also significant remaining patches of private ownership, primarily in Etobicoke, at Lake level; though substantially more if you consider land along the top of the Scarborough Bluffs.