Your route once you cross in to Ontario is a stones throw away from my second home. I have seen cyclists try to tackle some of those roads there, and I have thought about it myself also. The roads are scary to drive in a vehicle at times - let alone on a bike. A few people here have commented already that the roads can be crazy. You are riding through much of the Canadian Shield in the area around Winnipeg to around Thunder Bay. The Trans Canadian Highway, and any of the major roads for that matter, are cut where they can put them.

To add to the hazard on the Trans Canadian Highway is the truck traffic. You will find a lot of logging and mining trucks traveling through there - some think they have wings so reaction times are non-existent. The 2 lane roads like that are no place to be riding through. People do it, though, so to each their own.

From a fitness perspective - I would not recommend taking on such a long trip without a couple of riding seasons under your belt. You need to learn about your body on longer distance rides. Light cycling for fitness doing 20-30 miles every weekend or a few days a week is no comparison to packing in miles day after day, week after week. I am going to assume you have clipless pedals. After being in the distribution chain for bike parts I am making the assumption that you have some time cycling to some extent and you have good equipment. However, you need to start riding enough that you find your limits and weak spots. You need to do that for at least a full riding season to build your body up in the process, then use the following season to fine-tune.

The background to my above comments on learning about your body are the fact that I jumped through a few hoops adjusting myself and my gear to cycling. The first year I found a lot of "weak areas" and "limits" and ended up with the "phone a friend" call of shame to bail me out of a century ride attempt at 80 miles. After making the gear changes and building myself up to it the following season I was a lot better. The turning point to my end of the season was a 116 mile day tour (combined with a hiking trip in the middle) I completed successfully, only to have some pretty major knee problems shortly after that made riding a nightmare. I fought through, for better or worse, to close out my riding season with my mileage goal and finish the year with my winter backpacking trip in the Appalachians before I had my knee looked at. I started this year with an atrophied leg and several months of physical therapy trying to fix a problem my cycling caused. I never knew I was causing it until I had a problem and went to the doc to figure it out. The long and short of my problem was I was using platform pedals where I could only extend my legs to push the pedals. I couldn't pull up or move my feet/legs in any other direction or I would loose contact with the pedals. I built up the muscles and tendons to do that - and never balanced that with opposite motions.

So, my point in short - you need to get on the bike and get your distances/loads up to figure some things out. You need to know how your body is going to react and the only way to do it is to get on the bike and see what happens. Everyone is different. I do hope you work towards your goal and conquer it. Just prepare so you can succeed, and not shoot for the moon only to fall well short.