well I believe that the combo of a canister and an HOB filter is very effective.
Your whisper filter is for aquariums from 30gallon to 60 gallon. and your Fluval 105 canister is rated up to 25 gallons. Normally on this site it is recommended to have twice the recommended amount, so more filtration wouldn't hurt. But if you are consistant with you weekly waterchanges and keep a good eye one the tank, you should be able to do pretty good. If you got one more 30-60 gallon Whisper HOB... I would feel more comfortable saying your are "good to go"(about $35Bucks).