This is a drop-in bench-style canoe seat that should fit most tandem canoes. It has seen some use but is in very good condition other than one small crack that I have left unrepaired and doesn't seem to be growing (I can text or email you a pic). A small amount of superglue or epoxy would be an easy fix.
I've been looking for detailed specs online but haven't been able to find much other than a couple old webpages that I've linked below. I believe these were made under both the Carlisle and Old Town brands.
We used this to seat two kids side-by-side until one graduated to bow paddler. Now that the other has also graduated to bow paddler it's time to pass this along to someone else. Not sure what a reasonable price would be but I believe it retailed for well over $100. I'll start at an asking price of $50. Local pickup (Brainerd, MN area) would be ideal but I could look into the shipping cost if someone was interested.
Carlisle snap-in center canoe seat (REI) Carlisle snap-in center canoe seat (ACK)