It's super-tough to do because the bodies of water are separate. If you were able to combine the tanks so water can level out between the two, you'd be better off.
When it comes to filtering two tanks with a single canister, there are two key problems that are tough to overcome because nothing is 100%. If one half of the intake is dirtier than the other or becomes clogged, then less water is going to be pulled in from that tank. That's going to lead to overflowing in the other. There's also no way to really guarantee that your output is going to disperse equal amounts of water into each tank.
Regarding the sponge filters... it will be next to impossible to really control the amount of water moved back and forth between tanks. Folks who have used those in such a manner in the past did so merely for water movement.