If you're healthy, you've got the right body.

At 6'0" 210 lbs, I'm way too big to ever be competitive as a runner. But I like running, it's good for my back, and unlike all the competitive runners I've known, I don't have knee problems, achilles problems, stress fractures, etc  etc. So I'm not complaining.

I am another who hikes and canoes. I think you will find the portages in Q really easy compared to backpacking, even though your load might be a bit heavier. No quad-killing 1000 m elevation gain switchbacks for example.

For me, it was always a struggle to get away from the every-ounce-counts backpacking mentality, and accept double portaging as no big deal. DD's weight limits are about right for me too (hiking and portaging), so don't feel intimidated by the voyageur numbers you read either !

None of the portages on the route you mentioned are killers. Check QJ's portage database for details: sometimes not all maps show the portages correctly. I think one of the portages south of Jean was shown way off on (?) the Fisher maps, and I lost a half-day once because of it.

All of your wilderness backcountry skills are still valid in canoe country. The only difference I've found is a lot of the regs use waterproof plastic barrels for food storage instead of daypacks. You can spend money on them (REI etc), or sometimes you can get something just as good for free from Greek food stores who import their olives in throwaway plastic barrels which work just as well.