Hi Tor.......Good idea.
I'll kick it off with my arrangement for the Cape Fear.
Pretty straight forward....and bearing in mind that its a low on the floor kayak seat rather than a raised canoe seat....

I've found it infinately adjustable to accommodate any circumstances.
With a load (or tandem paddler/passenger forward) the rear seat is positioned right back against the bulkhead.
When paddling solo and no load forward, adjusting the straps on the seat brings it closer to the centre to balance trim better.
I
was going to add extra clip on points but have found that there's enough adjustment in the straps with the existing ones.
The 9mm ply board is about 4 feet long so there's plenty of scope. The second paddler/passenger board (not shown) is just big enough for the second seat.
It's usually positioned just forward of the thwart but can be located further forward if needed.
(I forgot to note on the photo that the boards aren't fixed in and just lift out)
I guess for a canoe, you could have a similar setup with a raised seat attached to the board as one unit...and probably clip on straps from seat to gunnels for side to side stability...(?)
John.
1 Cape Fear Sit In....a couple more planned
2 Laker 14's
1 Paddle board
"People who don't make mistakes don't make anything"