With a 40 i wouldnt recoment a fluadized bed as it wont be able to hold enough media for it to be sufficient for that size of tank.
There are two option that you can go with.
One is a wet/dry, you would need to build a trickle tower which is easy and there is plenty of videos out there that show you how to do it. The benafit of this type of sump is that it allows for more water from the tank to go down into the sump in event of a power outage. The downside is that it is less water volume meaning less stability.
The second option is a submerged sump in which the media is completely under the water. This is a far simplier design that allows you to have alot of filter media and water volume then a tricle tower but the downside is that it doesnt have the space for the water after a power outage, you have to be alot more cautious when designing the sump to make sure that you have the space for the water.
On another note you can use that canister filter as an addon to the sump, allowing you to have either more mechanical filtration or more biological filtration. Personally i would have the input of the filter in the last chanber of the sump and the output in the first chamber of the sump allowing you to circulate more water through the sump.
I hope that this has helped and i look forward to seeing what you end up doing.
Good luck.
Thomas
