That's... a pretty bad comp. You really don't have any decent healing with that group. If the other team sees no healer, all they would do is play conservatively and whittle down the HP of either the mage or the hunter. Prot pallies seem like they would be good in arena, but all pallies have the issue of gap closing, and your prot is going to run out of mana without a healer. No Lay on Hands in arena either.

An opposing team would CC the pally and then go one of two ways: Kill the pets for a slow and steady victory, or go for a burst, probably on the hunter. With 2 dps, they should be able to gap-close on the hunter and burn him down without any real issue, and since they have a healer, whatever damage you are doing is going to keep them topped off. They could also just chain CC you guys until your prot goes OOM (which will again be very fast without a healer), and he will be completely defenseless.

The only way I can see you possibly winning is if you use Water Elemental Freeze from max range and just tunnel down their healer with the mage and the hunter, while the prot keeps the other players occupied. That would be a very bad team that would let you do that though. Prot pallies are really awesome in BG's, but 1v1 are terrible (especially against a spellcaster), and without a healer they are really nerfed.

Bottom line: A 3's team without a healer is tough enough, and the classes you listed don't have any really good synergy to overcome that.