I wouldn't buy a "cheap" canister. You'll end up with problems down the road (i.e. dead fish, fouled water, broken parts). I suggest you break the bank and buy a good canister... it will save you big money later on. If you don't want to bother with the canister (although it's a good idea with plants), get the powerhead and keep your cheaper power filter.
I heard they are a good canister (although I prefer Eheim) and this one is fairly inexpensive. I don't know how big your tank is, but you will find out quickly that a good canister was well worth the money.
I would definitely use a marineland pengiun or even better an emporer. Since your tank is planted and you're using C02 I would just fill the tank up to the very top so that the filter wouldn't break the surface of the water. I also know a trick with the pengiuns to reduce filter prices, go to wal-mart and buy the filters for the aqua tech brand filters. they fit perfect in the pengiuns and the are half the price. :thm: _____________
I like the aquaclear the best. But also use an emperor 400, penguin 150, and whisper 200 (?). They all work, and are a LOT easier to service than the cannister filters.