Hyway 17. Through Ontario.

Highway 17 is the TCH and is highly developed and well maintained option to the 400 series roads.

This is posted on another RV site.......FYI.......

Avoid HWY 17 WAWA to White River

For those peoples travelling through Northern Ontario, be for warned. The section of highway 17 (THC) is being blasted, repaved and culverts replaced; between Wawa (on the east) and White river (on the West). I drove my coach though an area that is gravel only (10 km) and it completely covered my coach with mud and dirt. Not to meantion the amount of stones bouncing off the coach. I slowed down as much as possible, but still made and incredible mess. Bst bet is to take highway 11 and go the Northern route.
If you don't mind travelling on gravel road then the 1 1/2 to 2 hour delay for the construction may change your mind.
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Thanks. If we do this it will likely be in October. Perhaps the construction will be complete. We would like to cross on the ferry at South Bay Mouth. Couldn’t do that if we went the northern route.

Came through Hwy 17 last Saturday and Sunday from Thunder Bay going south with no problems to speak of. Blasting is not an issue and traffic was excellent except for maybe 3 bridge construction lane closures of maybe 5 minutes each. Found no stretches of gravel whatsoever. No reason to avoid.

The section from Wawa to White River was bad in July when we went west but better when we returned a couple of weeks ago. The RV has a bunch of road tar on it, it will take a pint of WD-40 to take it off from the July part! If you are going later the "construction season" may be quieter!