For tripping, I prefer a canoe regardless of whether you’re solo or dual. It’s just so much easier to pack, and especially for portages - with a kayak you have to spend a bunch of time unpacking and repacking. In a canoe, you can hop out, sling your pack on your back, roll the canoe up on your shoulders, and walk. And the other advantage is that because it’s not as space restricted, you can use a proper frame pack, which will make your portages much nicer.
Dom, I am nowhere near able to answer your question(s), though I have paddled both a little bit.
But I am wanting to point out this book to you about Canadian Don Starkell who took a sea kayak from Hudson's Bay (I think he started in Churchill, MB) and over the course of 3 summers paddled around the northern coast of Canada to Tuktoyaktuk (or "Tuk"), Northwest Terrritories. He couldn't go in winter because the sea was iced through. You might find this an interesting or inspirational read. I recall his description of being chased by a hungry polar bear who was swimming after him for hours while Don paddled his kayak as fast as he could for those same hours. Eventually the bear gave up.