Since we can't get into their heads, and there is no real consensus regarding whether or not whales and dolphins really have human-level intelligence, I would argue that an animal must be able to manipulate its environment (while at the same time being able to do other things like move, breathe, eat, and communicate) to become highly intelligent in a human sense. Humans did not evolve intelligence until a permanent upright posture freeing the hands was achieved. With fairly minor changes possible candidates for evolution to human-level intelligence could be (or could have been)
bipedal dinosaurs with grasping hands
elephants or other animals
another variety of ape or monkey
octopi and squid
animals with prehensile tails
bipedal dinosaurs with grasping hands
elephants or other animals
another variety of ape or monkey
octopi and squid
animals with prehensile tails