You won't be able to use a HOB (hang on the back) filter since most water areas aren't going to be within a few inches from the top of a tank. You could use a sponge filter but in general those need quite a bit of depth to use and wouldn't off much for such dirty frogs. I only use large sponge filters in my fire red cherry shrimp tank.

As for canisters, I only use generic ones, most of which are manufactured in the same place the big branded ones are. I used to be a fluval only guy until I needed some filtration on a budget and these work just as good if not better plus a fraction of the price.

Check on ebay for sunsun or jaebo canister filters, these are amazing off brand filters. I own both brands and they are running strong with no issues.

This is the exact one being used in my frog tank. Amazon.com: SunSun HW-302 3-Stage External Canister Filter, 264 gph: Pet Supplies
I got mine on ebay though for about $36 best buy ive ever made.

I leave my out take tube half in half out so there is some surface agitation (with waterfall sound) this keeps any films from forming on the surface and I think moves the water a bit better in partial water areas.

Now my frogs stay in the water 95% of the time, only to come out for food or sometimes to burrow slightly in the heat bulb. My water stays a steady 78F with the new heater.