They mentioned Le Pacte des loups (Brotherhood of the Wolf) in some interview before BaW was released and after playing the expansion I can definitely agree there are some similarities.
Namely, the local populace believing the beast was divine punishment for them not respecting the traditions, and to a lesser degree, the killings taking place in a region of Gevaudan (southern France), the same part of France Toussaint was inspired by, so the scenery looked kinda similar.
But, the most obvious source of inspiration wasn't any movie, but The Lesser Evil, a short story from The Last Wish.
for some reason I got the feeling that it borrows some stuff from Dan Brown's "Inferno".
Sienna's pretty much the "villain" in the movie, Syanna in the game - both characters have a hidden agenda and the material tries to somehow lure you away from their intentions in certain points of the plot.
Many assassinations happening across the city, each one focused on punishing people for their crimes, on a way that combines with the crime. A guy punished for gluttony would be forced to eat till he dies.