I've never seen a sump that wasn't divided, even on freshwater. I imagine that's because the division allows the water flow to not disturb the substrate, which was heavily planted with fast growers to help with nitrate removal, and had another division going to the return. I don't know how many bioballs you're talking about having, nor do I know how much space you'd have for them if you get dividers installed. I've seen other forums that had pictures of freshwater sumps, but they're much less common than saltwater sumps.
As for canister filtration, I'd recommend a filter that's rated for at least as much volume as you'll have. For you, that would be a canister rated for 125 gallons or better as a minimum. Now, be warned that this means they can get pricy. Sun Sun HW 304/AquaTop CF500 I think are both rated (basically the same filter from the same parent plant with minor cosmetic differences) for 125 gallon tanks, and they're in the neighborhood of $130, I think, because it's considered a "cheaper" brand. On my 55 gallon freshwater I have an AC 70 HOB (upgrading it to an AC 110 at some point in the future) and an AquaTop CF400UV, rated for approximately 70 and 90 gallon tanks, each, if I recall correctly.
For what it's worth, I think a 29 may be bit unsuitable for a sump for a 90 gallon tank. There's quite a bit of debate and many differing opinions, but the general consensus seems to be that a sump needs to be 50% of the volume of the tank or better. In the case of the 29, it would seem you would want additional filtration, because even with the wonderful biological filtration capabilities of a sump, it can only filter so much water at a time.