I'm running a 120G with Discus that I feed heavily. I run 1 2028 for biological and a magnum 350 for mechanical filtration. The magnum gets changed bi-weekly and the Eheim monthly. I am also using two 300w hydor in-line heaters. Works fine. That said though if I had to do it again I would definitely go with a sump.
If you still want to run canisters though then I would run at least 2 2028s. However whatever you do you want your water turnover rate to be at least 300 to 400 GPH. The more flow the better.