Matthias Schoenaerts spent two months boxing and eating junk food like burgers, ice-cream and pizza in order to gain weight and a little belly, because Jacques Audiard wanted Ali to look strong but not fit, a bit unhealthy because the guy is poor so he doesn't have the means to feed himself properly.
Katy Perry's "Firework" which features during the scene of the killer whales show, is actually a song that is played during the show that happens at Marineland, in France.