There's nothing wrong with a canister filter. You need to make sure it's rated at a minimum of 1000-1500 liters/hour for that size aquarium. I personally believe two canisters rated at the low end of that range would be best. The single most important aspect of any filter is the amount of media it can hold. Two filters would provide more media volume and also provide backup should on of the filters fails.
For a 55 gallon tank I'd go with an undergravel filter and a powerhead. You couldn't use sand as a substrate, but gravel is preferable anyway, except for very specific use cases. If you keep your stocking levels low you could get by with nothing more than an air pump. The only maintenance required would be weekly gravel vacuuming while doing your water change.
I'd also mention that danios aren't the best choice for gouramis and neons. Danios are extremely active fish. I personally would go with cardinal tetras rather than neons. They're hardier and more colorful. I'd also add a small group of corydoras. I think a pair of dwarf gouramis, 3 or 4 of the smaller corydoras species, and maybe half a dozen cardinals would make for a nice community. Some people may tell you to add more fish, but I'm a firm believer in maintaining light stocking levels.
I agree with under gravel filtration but I'm old school. If I were to, again, setup under gravel in a 55 gallon I'd do the same as I've done before. Use two filter plates with two air risers on each. Use air and a stone on one riser for each plate and a power head on the other riser on each plate.
Yes, sand cannot be used with this filtration as it will just sift down through the filter plates but there is gravel available that is fine enough for corries and plecos yet large enough to not go through the filter plates. Not saying that is is always easy to find but it is out there.
Most people consider under gravel filtration obsolete and I guess it probably is but people here put up with me as I'm an old guy that is stuck in his ways.
They just put up with my quirks.
Yes, if there is a LOT of over feeding and such and the under parts of a filter plate gets a bunch of garbage it can be a pain to clean out but there is an old cheat that allows doing this fairly simply.
1) Get two plates that are sized to leave a space between.
2) The plates will have a bunch of pin type supports to support the substrate. Snip off some of these 'pins' to make channels. Some filter plates will have open sides and others solid sides. If solid sides plates for a 55 gallon will probably be tall enough to cut openings that would fit a 3/8 inch air line. Cut 4 slots to fit the 3/8 inch line on the side that will align with the channels made by snipping the support pins.
3) So now we have filter plates with side access for a 3/8 inch air line with channels made to allow access for that same 3/8 inch line. To clean under the plates you just feed the air line through and siphon just like you would for vacuuming the substrate from above.
I have actually done this in the past and it works to clean under the plates without breaking down the tank. To be honest, unless very much over feeding, and not doing normal maintenance, the most I've really drawn out from under the plates is some slightly brown water with just a small amount of sediment if done twice a year.
So why am I an advocate for under gravel filtration in the first place? While we will never actually achieve, we are trying to duplicate nature. Whether the fish we allow to control our lives are naturally living in lakes or rivers a LOT of the water in their environment goes through the river or lake beds. In my humble opinion under gravel filtration does the best to imitate this as the water is drawn through the substrate imitating the flow through the river/lake bed. I personally consider this important if fish are being kept that would naturally live in a river. If lake fish this is probably much less of a factor.