Actually, no. A canister is not at all necessary for a 55. An AC110 will handle a 55 just fine. If you want to keep life simple, in terms of maintenance, put two AC75 and you're good to go. Its always better to have multiple smaller filters on a single tank than one large one, just to have as a back-up for times of maintenance and/or failure of one of the units.
If you're set on using a canister, then the Sunsun 304b will be fine. I own 3 of these units for a couple of years now, and have had no issues, so don't let the price deceive you
