I agree with others who recommend taking the Go train out of Toronto.

When heading east, I have taken the train to Rouge Hills, or even to Oshawa, as a way to avoid traffic. Although it is possible to cycle through the streets of Toronto to exit the city to the east, it is not pleasant. As you are undoubtedly aware, Toronto has an embarrassingly underdeveloped cycling infrastructure. Holland, this is not!

I have gone west, beginning from Mississauga, along the Waterfront Trail. That route was fine. I have also traveled north and west in the direction of Brampton along Steeles. I would not do it again. In fact, I bailed when I arrived in Bramalea, and jumped on the Go train. The fast-moving cars and trucks, and total lack of cycle lanes, defeated me!

Once out of the city, however, there are wonderful rides to be had: the country roads around Elora, Milton, St. Jacobs, Georgetown, the forks of the Credit River, are top-notch. Going east, Prince Edward County is a jewel, a true cyclists paradise. Once you are out of Toronto and traveling east, the Waterfront Trail is fine, although sections of it are on the 401 Service Road. I am particularly fond of the lands north of Kingston, including Sydenham, Desert Lake Road, Holleford, and Westport. Along Holleford Road there is a giant meteor crater, the result of an impact 350 million years ago. You kind of need to know what you're looking for to spot it, but there is a sign by the side of the road to point out the impact point.