We did the northern part of the great circle a few years back, it was a great trip. We started in Thunder bay staying at the Fort William Historical park. We spent a few days checking the park (great place for history) also a short distance to Kakabeka Falls another great place.
https://www.ontarioparks.com/park/kakabekafalls
From there we traveled east to Wawa for an overnight stayed at a great little park
https://www.campinginontario.ca/Wawa...tAndCampground
Heading east to Nigeria falls. Just a word of warning from Wawa to Niagara Fall there are NO gas stations, fill up on either end.
As for door county my favorite spot is Hyland court RV park
https://www.hylandcourt.com/ Its easy to spend 4 or 5 days in door county. If you like smoked fish get it from the shop at Gills Rock. And do not forget the famous door county "fish boil"
Good Luck safe travels