The culture that Sokka and Katara hail from, the Water Tribe, is clearly modeled after real life Inuit cultures of the Arctic region. The Last Airbender's production designers obviously agree.
These are the Inuit skin tents that they're emulating:
These are the people who lived in those tents:
These are their modern descendents:
And this is who Paramount Pictures cast to play Sokka and Katara:
The cultures in Avatar: The Last Airbender may be part of a fantasy setting, but they are explicitly based on real cultures that exist in our world. Paramount is appropriating Inuit culture and populating it with caucasian faces. We could not disagree more with that decision.