Generally, for any tank larger than 30 gallons, I would usually suggest a setup of multiple filters. For your 90 gallon tank, I would put a prefilter sponge over your canister's intake and dedicate that completely to biological filtration (ie. stuff it with as much biomedia as you can, rinse out that prefilter once a week). Then I would add one of the following extras:
1.) One Aquaclear 500 (or equivilant)
2.) Two Aquaclear 300s (or equivilant)
3.) Another smaller canister. Once again with a prefilter over the intake.
Options 1 and 2 is assuming that you'll have no plants in your tank. I choose aquaclears because of their relatively large media basket. So you can stuff those with filter floss/sponges for good mechancial filtration.
Option 3 is assuming that you will have plants in your tank.
I would personally choose option 2. 2 filter is better than 1, so its logical to say that 3 filters is better than 2. I wouldn't worry too much about too much water flow... unless your fish are extremely sensitive to water flow, most fish can handle a bit of moving water.
Keep in mind, the options I gave you aren't set in stone, they are a lot of ways to filter your tank... I just gave you what I would personally do for a moderately stocked tank.
HTH
-Richer