Tank size is 120 or so i haven't gotten that far i just know the minimum is 120g the tank will house 2 dempseys one convict 1 Oscar and one pleco. and the only pland is an anubius Batari
Anubias are very undemanding. If there are more plant species in your future, and lots of lighting, I'd go canister. If all you want is big fish and a plant or two (like Anubias), either will work (though sumps are generally noisier and lead to more rapid evaporative loss).
sumps are very under rated in the fw. though its more of a diy your type filter. with anything that big i would look into both. a sump with a canister back up.
The biggest advantage to using a sump is the additional water volume it creates. With your fish choices I would seriously consider a sump. It has other advantages as well- you can put your heater into it, you can dose ferts and meds via it and they can hold much more media than other types of filters.
The downside is the plumbing, the fact that you are working on it at floor level and the initial cost/effort to setup.
I agree with Mg in saying you should consider both for your particular situation.
I don't really care to much about the anuibs i don't really add anything to the water for it. It is attached to a peice of drift wood. What i really want is filtration the will keep my water very clear and filtered well. I don't know much about sumps. someone told me that i need a bioball sump. I know what bioballs are but that's about it. i don't really want to get a tank with a built in overflow and all that it ups the cost so much. I wa thinking about an eheim canister.