"Wolf lay there on the foot of Geran's bed looking at the dying fire in the fireplace with those golden eyes of his for quite a long time. Everything seemed to be as it was supposed to be, so Wolf sighed contentedly, stretched his muzzle out on his front paws, and went back to sleep."
This is the last paragraph of Polgara the Sorceress, and the last words in this whole story (note: emphasis mine). The implication is that somehow Wolf knows how things are and are not supposed to be progressing now that all the prophecies have been fulfilled and Cyradis has made her choice. This is what implies that he is more than just a run of the mill wolf, since presumably normal run of the mill wolves living the forest don't have the power of clairvoyance.
Suggestions people have made: Precursor to dogs? Well dogs appear numerous times in all the books of the Belgariad/ mallorean universe, so that's not it.
Aldur in disguise? Possible, though Aldur usually appears as a human (the funny old man with the cart), and the Gods, except for Eriod are now apparently going to start extricating themselves from this world, though I suspect that would be a lengthy process.
Embodiment of the prophecy hanging around??? Perhaps, though it doesn't seem to really have a need to have a body all of it's own, remember it's lived inside Belgarath and Garion, and Brand (the one at Vo Mimbre) amongst others. I would suspect that such a powerful entity wouldn't really need a body simply in order to check on the progress of things, which is all that seems to be happening there, it would just simply look and find out, it wouldn't have to go to the trouble of inhabiting the body of a wolf.
The wolf is not Poledra's child in anyway (though that is an interesting idea, though would sort of mean that Polgara has a brother), she states quite clearly that she just found the puppy, and felt that she couldn't leave it to die a lonely painful death.
Regrettably the real answer (if there even is one) is that we will never know, since both Mr and Mrs Eddings are no longer with us, for us to pick their brains and harass until they finally tell us.