I know nothing about using a canister in lieu of a water pump, do sadly cant help there
i had a 75 gal tank running a small sunsun filter, when the turtle was small it did the job but a year later and it was time to change... I found a fx6 and it has been awesome for the past while... Now that I have upgraded to the 125g and have a little more undertank room looking to add the sump to act as a prefilter for the fx6... I wish the "new" tank was drilled but it isn't... I have seen a few diy pvc overflows and looking to try something like that and as you see the tank is not full so a standard hang on back overflow will not work...