My chronic back pain (osteo-arthritis) is made worse by paddling a canoe while sitting -- whether I have a seat back or not.
A butt planted on a seat with knees bent or straight to the front can not offer the leverage needed for correct paddling.
In a canoe I always kneel and only support my butt with the front few inches of the seat. Before deciding to kneel, I was all over the seat trying to find a comfortable position -- it only screwed up my paddling technique. Since deciding to kneel, I have become a better canoeist. One must have a forward lean to correctly paddle a canoe -- not a rear-leaning backrest.
Hmmmm, maybe that's it. Does taking a "canoe ride" make your back hurt? Use a seat with a back. Does canoeing make your back hurt? Change to kneeling.
In my kayak, I sometimes feel a back pain coming on. Then I realize I have lost my paddling posture and I'm leaning back on the coaming rather than sitting corectly and using the lumbar strap for support.