I applaud you on your effort so far. From experience I can tell you that going over the top of Lake Nipigon is difficult to say the least. A bunch of us from Thunder Bay have tried 3 times via 2 different routes and been successful once. Different maps show roads but most have long since grown in or had there bridges removed or washed out. We learned of a new route last summer and tried but gave up due to the cold, being soaked and to much water and way to many bugs .
The spots that are hard to get over are around 350 km north west of Thunder Bay. You're a long way from help if someone gets hurt.
That being said we intend to try again this summer if the weather will co-operate
You might consider the old CN rail line from Geraldton to Thunder Bay and than up to Sioux Lookout. Some really scenic stretches and from Thunder Bay to Sioux Lookout you can cruise at 100+ kph if you want.