What is the difference between carnivores and cannibal animals?

Carnivores means meat eater. An animals that hunts and kills for his own meat to eat is both a predator and a meat eater. An animal that (mostly) searches for meat off already dead animals is obviously a carnivore, byt doesn't have to be a predator.

Vultures for instance do very little - if any - killing themselves, but are quite happy to pick the bones Clean of any carcass they can find. Might be an animal that has died of natural causes, or the leftovers after a lion's meal.

All carnivores are predators, but not all predators are carnivores. Predators eat meat, but carnivores eat exclusively meat.

So while humans are predators, we are not carnivores, because we also eat plants. Sharks are both predators AND carnivores.

"Predator" is also typically used in relation to their "prey." For example, a spider is the predator while a fly is the prey. Carnivore isn't usually used that way.