http://www.gear4portaging.com/
This seat back allows me to move around and not have the back interfere with paddling. Since my canoe has a bench seat and wood gunwales, the connection is a little different than if you had a canoe with bucket seat and aluminum gunwales. Here is a how it looks on a wood trimmed canoe with bench seat. The seat pad is made by Skwoosh and is independent of the seat back. I added a thick mini cell foam pad under it to give me a bit more height in the seat.
The seat back adjusts up or down via a simple strap adjustment and rigid stays. A long strap goes around the seat frame then up through the top buckle. A thumb loop pulled down adjusts the height.
The bands that connect the backrest to the boat come with a D-Ring. I had Kevin of CVCA just send me a simple stainless washer as the D-Ring is not corrosion resistant. I removed one of the screws along the gunwale and replaced it with a longer one to compensate for the material thickness. With an aluminum gunwale you would have drill out a rivet and re rivet the strap to the gunwale.
For car topping you can unsnap the seat but I find it easier to cinch the front straps and bring the seat forward.