I'm planning a weekender tour along the north shore of Lake Ontario to Kingston, Ontario.
The Waterfront Trail at least from Toronto is all secondary roads and paths east along the lake. A nice provincial park is located on the route too. I will be staying there.
I've done the route from Toronto to Kingston and area a few times, and agree that it's possible to avoid heavily trafficked roads, at least most of the way. I'm not sure it qualifies as a "low-stress" trip. I got a little nervous cycling past a nuclear waste facility, near Pickering or Darlington, I think, especially when I noticed that somebody had cut holes in the metal fence!
Getting out of Toronto is no picnic. Better to take the Go Train to Scarborough, or even to Oshawa.
It may be possible to do the trip in a weekend, but you'd need to ride quite fast. It took me four days.