You don't need a canister if you have a sump - google DIY sumps it should give you all the info you need. Basically you will need to either drill the tank ( if it's not already) or you can buy a hob overflow to drain into the sump, then a return pump to get the water back into the display. Sumps are great because you can put you water and skimmer in there and out of the display, they can include a refugium where you can grow macro algae too. You will still need some flow in the tank and depending if you want reef or fish only the lighting will need to be researched too. Do you know what you want to keep? Check out liveaquaria.com for fish selections, tank size and compatibility.