Its a bit hard to tell what roads are and are not paved based on goggle maps. you can sometimes tell with the satellite shots. For the most part, the roads that are yellow are the busier 'country' roads. i would stay off of Highway 5 (dundas), 6, 8, 25.

From what I've been told you can pretty much ride from hamilton to cambridge via the rail trails, althought I have never done any of these sections. The rail trails should provide better grades than the roads, the surface wont be as smooth (crushed limestone).

There are many quiet roads to take to get to Kitchener, most of the 'Lines' and 'sideroads' are great for cycling. The roads can be quite hilly between the escarpment and the kitchener area, with the escarpment being the biggest climb.