I did this very trip last year and had a great time. It's part of the 'Great Spirit Circle', quite a few Indian reservations along the way.
The only busy areas I encountered were on Hwy 17 east of Espanola; near Sudbury; and some traffic around Muskoka. Hwy 69 is busy, but has a really nice 8 foot shoulder, except for about 20 shoulderless kms south of Sudbury. From Parry Sound south Hwy 69 becomes much quieter because traffic is diverted to the new Hwy 400.
The terrain is mostly flat to rolling. The hilliest part was the La Cloche mountains just north of Manitoulin Island; not overly difficult. Other than that, just a couple more thigh burners.
Services on that route are reasonably plentiful. Almost every day I passed through a town or city that had some sort of B&B, motel, inn, restaurant and/or grocery store. Places like Owen Sound, Wiarton, Tobermory, Manitouwaning, Little Current, Espanola, Sudbury, Parry Sound, Muskoka, Orillia and Barrie. A fairly good number of campgrounds in the area btw.
I could give you more info on the best roads to take if you want. Just let me know. Cheers!