On the DVD of the movie, one of the Deleted Scenes in the “Extras” showed that they shot a scene of actual Christians being forced to die in the arena, and they show the hero, Maximus, watching this scene.
All in all, I think there is no doubt that Maximus is never depicted as being a Christian.
Recall that his personal motto in the movie is “Strength and Honor.” That is very Roman. No very Christian.
Plus, per my understanding, at the time period the movie is set in, NO Christian would have served as a General in the Roman Army.
Yet, I hold the view that the Maximus character is very Christian-like in some ways.
But in other ways, he is not. As I recall, Maximus tells the evil Emperor at one point, “I will have my revenge!” That is NOT Christian. At least a big part of the motive of Maximus was getting revenge for the murder and torture of his wife and daughter. He clearly had other motives too, eventually, however.
Yet, in my view, Maximus was working for a political solution to the world’s corruption. As such, Maximus is like the political Messiah that the Jews in the time of Jesus were looking for. They engineering the torture and death of Jesus precisely because he was a spiritual Messiah, not a political Messiah.
Yet, even today, many Christians see Christianity as being mainly or wholly a Political Program by which to win the Culture War against liberals and atheists and secularists.