Traffic is pretty light on the 6 through Manitoulin Island, and the scenery is spectacular. The weathered-smooth granite formations here are unique and iconic of the Georgian Bay region. Along the Bruce Peninsula, traffic might be busier on weekends when people from the city come up, but otherwise the southbound traffic will have waves of traffic using the ferry. I would stay off the main highways south of Owen Sound, there are a lot of quiet county roads that offer better alternatives.
If you have fatter tires that can handle some off-road riding and don't mind a slower speed there are several rails-to-trails you can take some of the way.
If you are in Elora on a hot day, you might want to try tubing on the river. Guelph is a quaint-looking town