Is the Kohler canister a drop-in replacement for any toilet? (You said you replaced your toilets.)
The toilets that came with the house were either from the 70s or 80s. I wanted to replace them with elongated bowls and something with a 1.6 gallon flush (instead of a 3 gallon flush or whatever they were). I ended up getting a few of the Kohler toilets because they seemed to be the nicest for the money.
I don't know if there is a universal cannister replacement. I know the replacement seals I bought had 2 seals in them...one for Kohler and for American Standard, so at least those two companies make cannister style valves. If you look at the picture I sent, the cannister screws into the bottom of the tank...which means the size of the hole in the bottom of the tank would have to be right for it to fit.
Otherwise, just get a new toilet! The new Kohlers actually have a sensor that allows you to wave your hand and flush. I think it's touchless or something. (sounds like something extra to break, but great for germaphobes)