I sympathize w/the desire.
But a cursory look suggest to me that location isn't feasible w/o redevelopment of that site.
The creek there is deeply embanked/sloped.
The driveway (private) is narrow, up against the slope on one side and over-full parking on the other.
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Though further north, and not at the southern tip of the trail, this looks to be the most feasible connection to me:
View attachment 330396
Still needs to be acquired.
But its open land, no obvious user conflicts, the grade is gentle, no ecological concerns, and there is a path into the valley directly opposite.
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Using Streetview, one can see the route I note below is now encroached on, either by parking lot enlargement or vegetative growth.
But it still looks do-able to me with minimal disruption.
View attachment 330398
Longer term, I believe the existing 'informal' connection to Leslie can be regularized through redevelopment.
While a new trail into the Don, at that point is unlikely, there should be sufficient room in the Leslie ROW for a multi-use, off-road path running south to the existing Park entrance.
That room has been secured further south:
Leslie ROW runs to the pink line on the right/east side of the picture:
View attachment 330399
View attachment 330400
View attachment 330401
Then narrows here:
View attachment 330402
But way in which buildings are set back, plus the vacant land here, makes it fairly easy to make that happen.
(alternatively one could implement cycle tracks)
View attachment 330403