Ive done a bunch of what you want to do, but before I write too much in detail, what tires are you thinking of using?
Also, you've mentioned not being comfortable on quiet paved two laner roads with speeds of 80-90kph (50mph ish) , so is that true and absolutely something you don't like to do?
The Ptit train du nord surface is pretty much fine even with a road bike, the gravel sections are nearly all hard packed and fine, and there are more paved sections than in the past--very pretty route.

the inner Montreal bike trails and leading out of Montreal are really great and pretty riding all in all, Ive ridden most of them.

The Prescott Russell trail surface is mostly good, but when I did it about 5 years ago, some parts were looser, but I was on 2 in slicks and have ridden and toured on all kinds of surfaces, so was completely fine with it. I was coming from Ottawa back to Montreal, and was told by an oncoming cyclist that the start of it was much looser gravel (closer to the Montreal end), and I was leaving it anyway before that point to spend the night somewhere well off the trail, so I can't speak for that part (plus it was five years ago, might be better)

Look up stuff on this, and overall, I would suggest wider tires, at least 38--but then again, it really depends on ones riding experience.

The cataraqui trail past Kingston used to have some soft and loose bits, but I havent done it and what I just wrote was comments from a friend who did it a long time ago, at least ten years back, so again--look up info.
It should be easy enough to get some feedback online.

As for safety in campgrounds, do you mean from a theft standpoint, or bears and such?
As Canadians, we don't generally worry about "safety" as such, but I might be reading your question wrong, but there are not homeless people and that sort of worries in campgrounds , but you do of course have to use common sense about not leaving valuables out unsupervised, but more importantly use common sense about not leaving food out as raccoons, small critters and birds and can make a mess of things if allowed.
Again, not really sure the angle of your question and your traveling experiences, but overall, no you do not have to worry about safety.

feel free to ask specifics, I ended up writing more than intended.....
Oh, be aware that we have blood sucking insects up here in the Great White North, again, I have no idea of your experience with mosquitoes, black flies.