I did this a couple of years ago. You can avoid traffic by taking the bike path from Collingwood to Meaford rather than Hwy 26, and by taking the small roads that parallel Hwy 6 up the Bruce Peninsula. Take CR 1 and Grey Rd 26 between Owen Sound and Wiarton, and be sure to stop in Big Bay for ice cream. Hwy 17 is busy. Hwy 69 is busy, but has a wide shoulder for most of the way. South of Parry Sound I took smaller roads to Bala. It was pretty flat. There are plenty of services. My journal is here:
http://www.crazyguyonabike.com/doc/gbay.