So what I'm understanding is you want to hook them both in line to pull water through the pre filter and push it back up into the tank? Imho
, too much risk for something to go wrong.
The best thing about canister filters is that they hold tons of room for filter media. There's really no reason to over complicate your filter to add a little more. Just stick with the canister you want and arrange your media trays to filter how you want.