Unreal 3 is one of the most successful graphics engines of this generation, if not the most successful one. But we won't see it coming to the Nintendo 3DS, at least not according to Mark Reins who in an interview with Gamasutra said that he don't think it's powerful enough to handle it.
He did point out that they don't actually have a 3DS yet, but he believe that only furthers the point that it can't handle Unreal 3: ""we really don't know enough about it to make a formal comment, but I think if they considered that our engine would be good on it, they would have probably talked to us about it"