A dedicated frameless canoe pack is well worth the investment. When I was young, I used my framed backpack too, but it was too long to fit in a canoe crossways, and too narrow to efficiently use space along the sides of the canoe. The Duluth design (like the Superior One) is much wider than a typical backpack, so it fills most of the width of a typical canoe, and because there is no frame, you can usually squoosh it under a thwart if necessary to use the canoe's full length.

It sounds like you have a pretty good idea of the gear you like to trip with. So the main thing you want is a pack that's big enough that you can fill it up to your "maximum comfortable weight-carrying capacity", whatever that may be. Too small and you end up at portages with a light pack on your back, and a small, heavy bag of some sort in each hand: tiring, and with the increased risk of leaving something behind when reloading, especially if you're traveling with big groups.

If you're carrying a lot of kids stuff as well as your own gear, you may need two big Duluth packs. (Before you know it, your son will be old enough for his own full-size pack, and will be going off on trips without you, so you can give him the extra pack as a gift then :))

I like to have at least two pouches directly accessible from the outside at all times: one for clean stuff (maps, books, first aid kit, compass, etc) and one for not-clean stuff (rope, tent brush, latrine trowel, etc). I keep the clean stuff in a day pack and the dirty stuff in side pouches on my canoe pack, but as long as you have quick access to the stuff you need quickly and aren't packing dirty trowels in with your clothes, food/cookware and sleeping bag, how you arrange things is up to you.

Hope this helps!