A canoe pack is different from a backpack. Duluth Pack company President Tom Sega explains, “The canoe pack is what we were founded upon, they were the first products that were made at Duluth Pack by Camille Poirier…. When you’re canoeing you have to think about portaging, and when you portage a canoe you put it on your shoulders. So you can’t have a pack that’s above your shoulders. So canoe packs were built low – so they ride low on you – so that you can put a canoe on your shoulders at the same time… They were going to be in rugged country, so they needed to be built out of heavy duty canvas, so they’re built out of 15 ounce canvas. They also needed to be able to hold a lot of stuff; so how to you do that? You make them wide and you make them so that they will balloon out. The original packs were made out of an envelope, but even though you make an envelop pack and it lays flat, when you start stuffing it full it balloons out… And thirdly they were made so that they had to fit in a canoe so the would ride very low in the canoe and keep the stability of the canoe [good] by riding low and having your center of gravity in the canoe low.”
https://www.duluthpack.com/backpacks/canoe-packs/60-utility.html