canister = expensive all in one comes with pluming need a few
sump= can be done cheap, hides a lot of stuff, can over engineer, can flood
I like sumps as increases "volume" can hide all teh misc. stuff and you can "mix and match" your outcomes a lot more.
rememeber that mechanical filtration requires high volumes of turnover biological and SOME chemical filtration requires low volume turnover
CO2 can be put inline in either and have seen some nice reactors of late that woudl work either/or
Convert your 3 foot into a sump run canister on sump and have low volume sump to tank turnover
in effect giving you an 8 ft tank which gives you more chemical stability.a
light the sump and plant the bejessus out of it and use it as a refuge for or add a denytrifing coil and dont.
Lots of options