FAQ for
Terminator 3: Rise of the Machines (2003)

Several sources including Moviehole.net say that originally, Edward Furlong was asked to reprise his role of John Connor. However, citing personal reasons, Edward states that "it just wasn't meant to be." The largest rumor seems to be that Furlong's sobriety would potentially be an issue, so the producers opted for a safer casting in Nick Stahl as Connor.

The T-800 tells John that John and Sarah Connor merely postponed it and that Judgement Day was inevitable, and thus Sarah and John were in fact wrong in thinking they could prevent it.

This could be confusing, as The Terminator and Terminator 2: Judgment Day suggested the theory that "the future is not set", and "there is no fate but what we make for ourself". In this movie, the assumption is introduced that Judgment Day is inevitable, and that parts of our future are set.

The reasoning is that it is in people's nature to destroy themselves (also a quote from T2). In T2, John and Sarah Connor destroyed all technology that would lead to the creation of Skynet. However, scientists went on to invent Skynet without the benefit of the future technology that was left behind by the first Terminator. As Miles Dyson said in T2, the broken microchip and android arm gave him ideas, which caused him to invent artificial intelligence, but on an earlier date than originally planned. Without the chip and arm, he or someone else would have invented them anyway, but on a much later date.

So the Judgment Day in this movie is a different one than the one we see in T2. It is on July 24th, 2004 instead of August 29th, 1997. This also explains the differences seen in the technology (the Hunter-Killer aircraft are different, Arnold is a T-850 model Terminator instead of a T-800), which are the result of random factors, such as different persons designing them, the longer time of development, etc.

The inevitability of Judgment Day makes sense in a way. Remember that John Connor himself is a indirect result of it (the war against the machines prompts the Human Resistance to send Kyle Reese to the past, who becomes John's father). If Judgment Day was prevented for good, Reese would not have been sent, and John would not have existed. John's fate and that of Judgment Day are intricately tied together in that way.

John Connor was 13 in T2, and for a young teenager, the idea of leading mankind to victory against a violent race of machines in a post-apocalyptic world might sound exciting. We can assume that the care-free rascal John, at that point, hardly realized the magnitude of that responsibility. He got his first taste of responsibility when he ordered the Terminator to beat up two douchebags, and the android almost killed one of them.

Now imagine not being responsible for two lives, but several billion. As John says in the opening narration: "I feel the weight of the future bearing down on me. A future I don't want". They expect him to lead and to win. He has become older, and the full extent of what is expected of him has also become clear.

Every young person who is coming of age typically experiences some fear of the unknown future, and the fear of becoming responsible for the lives of loved ones. John needs to lead the remainder of mankind toward a seemingly impossible victory against a superior enemy. It is not hard to see how this causes him to get cold feet. Also, in order for him to become this great leader, 3 billion people have to die first, which adds further to his reluctance.

John lives in a mixed state of fear and denial. In the opening narration, he says "The future has not been written. There is no fate but what we make for ourselves. I wish I could believe that. (...) we stopped Judgment Day. I should feel safe, but I don't (...)." On the one hand he seems fully aware of things to come and his role in this, not believing Judgment Day was prevented in T2. But when he is confronted with the evidence for his suspicion, namely the appearance of another Terminator, his reaction is "You shouldn't exist. We took out Cyberdyne over 10 years ago. We STOPPED Judgment Day!" During the entire film, he makes every effort to prevent Judgment Day, ignoring the Terminator's repeated claims that "Judgment Day is inevitable", instead of preparing himself for the worst. John is clearly not yet ready for the truth and not yet up to the task.

So this change in John's character is not a break in character per se. John's struggle to accept his future role as savior of mankind was made an important part of the story. In the end, when it is clear that the future indeed can't be changed, John symbolically accepts his destiny, when the voice on the radio ask who's in charge, and he finally has the strength to say "I am".

There's a timeline difference with John Connors' character. In the second movie he was supposed to be around 10 years old, yet Edward Furlong looked closer to 13. How do you work that out as a writer?

MICHAEL FERRIS: You know we finally just decided to heck with that stuff because there were some unavoidable discrepancies between the age of the character of the second movie and this movie and the first movie. Three years is three years, what's the big deal, right?

Source: http://movies.about.com/library/weekly/aa070103e.htm

After Linda read the script, she described it as "soulless" and turned the role down. Another reason was partially because James Cameron didn't return.

Sources: http://www.imdb.com/name/nm0000157/news?year=2002 and http://www.ew.com/ew/article/0,,190090,00.html