Cleaning aside, the issue you should be most concerned with is circulation. Keeping water moving, both around the tank and through the filter, is what is important. I can't help you with which canister(s) to purchase, but I can tell you that as long as you have *enough* filtration, it doesn't matter if you have one filter or two. You can split the intake and outflow to mimic the function of two canisters, if you'd like. If you can find a canister powerful enough for your taste (one FX5 perhaps?), you can use a tee at both the intake and outflow, at two ends of the tank.
What I'm saying is that if you decide you don't need the power or filtration of more than one canister, water flow doesn't have to be an issue. Although the cost of the extra tubing, splitters, spraybar, and prefilter may be enough to convince you to purchase an extra canister with all the trimmings. Your call.