Well you need to distinguish whether you mean ritual cannibalism, cannibalism by necessity occurring in extreme situations of famine, and cannibalism by mentally disturbed persons.
I should think with ritual cannibalism, cooking is probably preferred, possibly with some seasoning and a side of salad or veg. For the latter, out of necessity or derangement, I shouldn�t think they have the time nor inclination to cook.
In the Pacific Islands 'Long Pig' was cooked with great ceremony and the only meat eaten with a fork as it was taboo to touch human flesh. But, apparently OK to eat it off a fork. I believe it was cooked wrapped in banana leaves in a long trench similar to a Maori oven. The people who prepared the dish apparently had special dispensation.