Here's an interesting interview with Jason Isaacs (Zhao).
IGN TV: They just announced that M. Night Shyamalan is doing a movie version of Avatar: The Last Airbender.
Isaacs: I saw that! I can't imagine they'll be coming to me, because as far as I'm aware, I'm the only Caucasian actor that does a voice in it. It was very odd, the first time I went to record. I looked around, and it was like I was in the wrong studio. I said, "Do you guys want me to do an Asian voice or something?" They said, "No, no, no. Just be yourself." And then after we started recording, they went, "Okay, just to slightly clarify that. Be yourself, but be your American self." I said, "Okay, fine." But you can't help but be influenced by the fact that all the other actors are Asian. I met the guy who plays Appa. He came up to me, a very cool looking guy, and he said, "Hey, how are you doing man?! We worked together." I said, "Really?" It's a big success, apparently! Because I've been in England, I haven't seen it or been aware of its success. I wear the T-shirt they gave me occasionally, and people come up to me and go, "I love that show!"
IGN TV: Well, if Night came to you and said he'd like you to be in the feature film, would you be interested?
Isaacs: In a heartbeat! I think he's a great filmmaker. I met him at the Harry Potter premiere last year. I was talking to him for about an hour, and he said his name was Night. I had no idea who he was! Only when I walked off at the end, I went, "Night... that's an unusual name... Oh my god!" I wanted to run back and thrust my resume in front of him, but it was too late. Probably just as well!