The Truman Show tells a story of a young man that is has been followed by cameras his entire life, because of the TV show. Ed Harris plays the director, the producers and the creator of this TV show.
His character is very calm and aloof. He does his job which is watching someone his whole life and he does it and acts as if there was nothing wring about that. He has taken somebody's life away and created it the way he wanted and he doesn't even have remorse. This stoic calmness is perfectly portrayed by Harris.
Everywhere he comes, the seriousness starts.
We could say that this behavior would be irrational in the real world. We also think it, till some moment in the film. It's the moment his character explains, why does he do this all. This is so much powerful moment. He says his reasons and Harris is so realistic and natural in this performance that we start to understand his behavior. He comes with so rational explanation, that for a moment we think that there is nothing wrong about what he did do Truman. This scene is very powerful and I would consider it his best scene.
From his character's presence we have a feeling that he doesn't absolutely care about Truman. But the truth is that he cares about him much more, than anyone. There is a scene, in which he comes to the TV screen, on which we can see Truman sleeping. Harris's character come to the screen and caresses Truman. In other actor's hand this would maybe look dumb. He acts as if he didn't care about Truman and then, when he's alone, he shows the opposite. This is a contrast and a twist from his previous behavior, but Harris handles is very well.
At the end I will only sum it all up. Harris didn't have an easy job playing this character. But he handled it with such an ease, that it could seem extremely easy to play it, which is not true...
The chances of winning an Oscar: I won't dare to guess. I think he wasn't a contender for a win, he was the third, maybe the fourth...