My responses...based on a moderate amount of experience.
1. No idea how plentiful low clearances are. They're something to be aware of, but it's not as though even the eastern US is so thoroughly littered with them that it's impossible to get around. At the same time, of course, it only takes one that you don't pay attention to for you to have a very bad day.
2. Yes, for the most part, some of course better than others.
3. It may be difficult to find full hookups with 50A power. Being able to deal with something lesser will open up many more campsites for you. This isn't exactly like boondocking, particularly if you're generally traveling rather than staying in one spot for a week or two at a time; you'll likely have water fill and sewer dump stations at hand. Using 30A or 15A power is really just a matter of putting on an adapter and being aware of your electric usage.
Some provincial and I assume other parks in Canada have shared electric boxes that can be some distance from the site. An extension cord will be helpful.
4. It sounds like a fabulous route to me. Don't underestimate how long Ontario is as you half-circumnavigate the great lakes. I think it's pretty close to half the Trans-Canada highway is in Ontario; it certainly seemed that way to me.
5. Usually you can get around okay with English, certainly so in the cities. The road signs are all in French only (or pictograms) but it's not too hard to translate, particularly if you know a few key words. For dealing with people, a good attitude goes a very long distance to paving over language barriers.