It depends on your stocking level and your ability to maintain the filters. To illustrate, you can filter a 400 with just a small sponge filter if you've only got a pair of guppies in there.
You know that the more fish you have in there, the more often you'll have to squeeze out the media in the canisters and the more hassle it'll be. And with a large tank like you have, I'm guessing you'll be stocking it with heavy poopers... which makes the sump really something to consider.
If sumps are out, then go for the most number of canisters you can afford depending on how often you are willing to clean them. In which case, FX5 or FX6 will be the way to go. I know Eheim has (had?) a massive filter comparable to FX6.... so if you have a large bioload, just scale up the number of canisters. Heck, slap 10 FX6s on there if the media is clogging too often... Sky's the limit!
Other option is you can make DIY canister filters out of 5 gallon buckets. YMMV on the long term durability/performance of these, though.
Enjoy!