Originally, Nicolas Cage turned down the role of Castor Troy, citing a lack of interest in playing a villain. However, once he was told that he would actually be playing the hero for a majority of the film, he quickly signed on.
The blood types for the two main characters (i.e. Sean Archer and Castor Troy)are mentioned in the movie, and at a subtle level they reflect their antagonistic nature. Archer's Blood type is O negative, while Troy's is AB positive, these two blood types are as different as you can get. O negative- the universal donor reflects Archer's role as a policeman dedicated to serving the community, while Troy's AB positive - the universal recipient suggests someone who takes from society without giving anything back.
The scene of Adam listening to "Over the Rainbow" on his portable headphones was John Woo's idea and not part of the original script. PARAMOUNT Pictures refused to finance the extra scene and John Woo had to use his own money to make that happen. He was later paid back as the film turned out to be profitable. (A similar scene can be seen in Woo's Hard Boiled (1992))
According to producer Barrie M. Osborne, most of the challenging action scenes, including the fight on the deck of the boat and the airplane going down the runway, were originally planned as green screen shots. But they filmed them practically to support the "realism of story".
The main character is named Sean Archer. Sagittarius the Archer, one of the constellations of the zodiac, is diametrically opposite (half-way around the year from) the constellation Gemini. Castor and Pollox are the two major stars in the constellation Gemini.
Unlike John Woo's previous US movies Hard Target (1993) and Broken Arrow (1996) and his later one Mission Impossible 2 (2000), Face/Off had little to none studio interference, and only scene that MPAA demanded to be cut was opening assassination scene where Sean Archer's son is killed.
Originally written in 1990, the script was first optioned by producer Joel Silver before falling into the lap of Michael Douglas who, the screenwriters fervently hoped, would star in it alongside Harrison Ford. Instead Douglas took over as producer with the roles of cop Sean Archer and villain Castor Troy eventually going to John Travolta and Nicolas Cage respectively.
In Greek mythology, Castor and Pollux (the two brightest stars in the constellation Gemini) were the twin sons of Zeus by Leda. The brothers fought together in the Trojan War (which, of course, was fought in *Troy*). This is not their only connection to Troy, their mother Leda was also the mother of Helen of Troy. Of the Castor and Pollux of mythology, Pollux was immortal and Castor mortal. They were allowed to spend alternating days together between the underworld and Olympus because Zeus took pity on the pair and "gave" Castor half of Pollux's immortality because they could not take the separation of death.
When Troy is attacked by the guards at the prison, he dodges behind a box marked "Ingen". That's the company that cloned dinosaurs in Jurassic Park (1993). "Ingen" also means "no one" in Danish, Norwegian and Swedish.
The ornate box that is opened for Castor Troy on the tarmac contains the following: a bag of blue pills, sunglasses, 3 rolled cigarettes(or joints), a pack of Chiclets, 4 pieces of Bazooka Joe bubble gum, a switchblade, and what appears to be a blue glass vial.
The other pairs of actors that were considered for Sean Archer and Castor Troy besides Schwarzenegger and Stallone and Harrison Ford and Michael Douglas were Bruce Willis and Alec Baldwin, Jean Claude Van Damme and Steven Seagal, Al Pacino and Robert De Niro.
Throughout the movie Sean Archer is shown to be physically superior to Castor Troy, whenever the two are engaged in hand to hand combat Archer almost always gets the upper hand, however Castor Troy has the better shot, he almost never misses.
The trivia items below may give away important plot points.
The special edition DVD contains several deleted scenes, most notably an alternate ending in which Sean Archer looks into a mirror, and Eve gasps as she (and the audience) sees Castor Troy's face as Archer's reflection. The studio nixed this ambiguous ending in favor of a happy conclusion in which Archer is definitely, completely himself again and Castor is dead with no chance of returning.
Even though Arnold Schwarzenegger and Sylvester Stallone were considered to play Sean Archer and Castor Troy and didn't get the shot, they later worked together in the Expendables movies and Escape Plan in which they both escaped from a futuristic prison like Nicolas Cage does in this film.
Castor Troy kills a total of 20 people during the course of the film (Michael Archer, Anderson, Montgomery, Berkeley, Pinkus, Genelli, Winters, Tito, Miller, Dr. Walsh, Dietrich, Loomis, Victor, Sasha, the owner of the boat, and 5 unnamed cops in the finale). Archer on the other hand only kills 4 people (Pollux Troy, Lars, Leo, Castor Troy).