You can really use any CFW you want. For the ones that don't have region free support built in you can just use Free Multi Patcher. Every n3DS CFW needs 9.0-9.2 I believe, 8.1 will not work. PastaCFW and ReiNAND are good options for n3DS.I looked it up, but the thread says that it doesn't support N3DS, unfortunately. Though since this new soon to come exploit, that might change.
Of course you will need CN to do that in the first place