How much LR did you say you have in there? If you have the right amount of rock per gallon then you may not need the canister. Putting the powerheads in there will give you more movement around the rock which should help in filtering. If you do decide to get a canister, know that you will have to buy the media for it.
They require cleaning as well, though you can take the filter pads out to help.
Fluval is good, I have a fluval 303 on my 55 gal reef. Do you have any other filters on that tank? And no I wouldn't worry about a mini cycle, your tank is still cycling, now would be the best time to put one in.