In the Rumble, it's going to be a Rock crowd just with the usual desperate for attention "heel fans" trying to start something. That Rocky-Cena chant was mostly from a few people in the front rows close to the mics, that's usually happens in a huge stadium. Alvarez reported back then that it was 95/5 and even kids with full Cena gear were chanting for Rock by the end of the match.
78k cannons going off at one time.
Cena: "The ovation when he came to the ring was the loudest I have ever heard"