Which brand and model canister filter would be best for a 210 gallon aquarium?

I always recommend buying a filter that is rated for around twice the volume of the aquarium. On a tank of this size I would personally choose a sump, however this means that the tank will have to be drilled for an overflow weir, adding to the expense of setting up the aquarium. You could take a look at the larger external filters such as the Fluval FX5 and the Eheim professional 3e.