From the looks of it they just shifted the races around
The thing is, all of the characters and cultures in the cartoon were Asian or Inuit. Nobody was white.
The other issue is that by casting white actors for the main heroic roles, and the prominent villain (and the entire Fire Nation) aren't. To better illustrate, here are a couple images from racebending.com
They're trying to make a movie that will be profitable and they apparently don't trust the fans of a cartoon to make it so. They took a risk and hired a nobody with no experience for the title character and are trying to save their asses by putting experienced 'names' in the other roles.
But I think even that dollar-focused-thinking is influenced by racist assumptions. It's the idea that white audiences can't relate, sympathize or root for characters/actors of colour, or maybe that the producers/movie Powers That Be assume that their only audience is white.
I think there is something seriously wrong on their part for assuming either of those things. I'd say that if they had cast the characters according to their original ethnicities, the movie would get more attention on top of avoiding the issue of racebending and offending fans of the animated show. But instead they actively sought caucasian actors.