Not sure how realistic this is, but I'm sold on the vision:
Yeah, I saw that.
So I had a look. The short answer is 'not very'.
This site has the Barrie GO Corridor at its western extent, which is a major barrier to going on to the Rail Path Corridor (along the Kitchener GO Corridor), which, in any event, doesn't go that far north yet), or to the Humber River, which is actually 2 Valleys over, The Black Creek Valley is the one immediately to the west, with Black Creek Drive in the way.
IF what he meant was connecting to the Rail Path via the Barrie Corridor, I don't believe that will be feasible with full twin tracks in place.
* Edit * Just checked, the corridor width drops to ~14M a bit south of Eglinton, a 2-track cross section needs about 11M, 3 leftover, including a sound wall, and/or fence is exceedingly tight. So I would say no.
Although..........most of the corridor has a cross-section of ~20M or greater, the choke points are relatively brief. But they would still require property acquisition. There is also the matter of bridging the major roads, of course.
Below is the straight-line distance from the site (Beltline Trail) to Black Creek Trail:
That's about 1.25km
Currently the only track crossings are at Eglinton and then Castlefield to the north.
This is the distance to the Humber Trail: (straight line)
That's ~3.7km.
That's across 2 rail corridors and the Black Creek Valley.
****
I do appreciate ambition; but unless they've come up with something truly creative, I would file this under hyperbole.