Although not a driver, I have had a long interest in geography and travel... Some time ago planned trips to places in Canada using Greyhound from within USA (but didn't actually get to do it, there were 'rover' tickets usable Mon-Thu at lower cost, and I thought I'd go from SFO to VC on Wed/Thu and return Mon/Tue as an example).
Anyway, long story short, I found that MapQuest.com handles travel directions.
Unfortunately while it estimates the time, it doesn't show times on the list alongside the places it names.
Found that on MapQuest, from Montreal to Kitimat, they offered choices for faster time or shorter distance.
I know you are breaking journey and why, but wonder whether going through USA is possible or just not an option. While it would add some mileage, it could cut down travel time (even avoiding toll roads). OK, travel documents, etc, may be too much to deal with, this close to journey, and customs / security checks could be awful as you are carrying clothes etc etc for that lengthy journey.
When I checked the options, staying in Canada took 60.5 hours and averaged 51 MPH, but driving around 1300 miles of the 3300 miles in USA, averaged 60 MPH (across the whole distance). Clearly to average that would need to be at higher speed for some portions and may not be comfortable or possible (depending on car, load, fuel efficiency, etc).
When you asked about 'driving for X hours' it hit me that it all depends on how fast you are allowed (and want) to drive (and load on the vehicle too, of course), plus any detours for road maintenance.
I know you have your list of places, and it may seem a daft idea to go through the USA for a chunk of the trip, but equally, with more populated route you would have more options to stop if needed, either to just have a drink/meal, or to stay overnight if you felt you'd made enough progress.
Staying within Canada...
From Montreal to Thunder Bay is almost 1000 miles, and the stretch from Sault S Marie to Thunder Bay alone is 440 miles, so that would fill a day of driving (about 9.5h on MapQuest).
So, you might want to do a couple of days driving for 6+ hours, then the long day to get to Thunder Bay, and then you're about 1/3rd of the way overall, and can cut down to whatever is comfortable.
Here are some possibles from MapQuest
Montreal -> North Bay, Ontario
7h / 350 miles
North Bay -> Sault Sainte Marie
6h / 270 miles
S S Marie -> Thunder Bay, Ontario
9h 30 / 440 miles