Thanks for the informed opinions. They are all very helpful.

That NRS harness is really cool. Mine will be pretty basic, but much
cheaper.

My pack bag is about 70 litres with a double-pull zipper from one end to
the other. (It's really just an old hockey equipment bag, but I think
it will work very well for this purpose.) The harness will be
completely removable, but I should be able to access the contents with
the harness on if necessary. I hope to be able to pack everything I
need for a weekend solo trip in that one bag. I'll still need to do the
portage twice, once for the canoe and paddles, once for the pack.

Tedr