How to spell Usanian (alt.: USAnian or USanian)

I more and more often see the world Usannian (alternative written: USAnian or USanian). This is used in spoken language and on the internet. It appears to be synonym with a U.S. citizen.

Consequently, Usanians is used to name the whole population of the United States.
www.usanian.com shows the context. What would be the right spelling of the world: Usanian, USAnian or USanian? Probably would Usanian be sufficient and work well together with other American populations, e.g.: ?

Canada --> Canadian
U.S.A. --> Usanian
Argentina --> Argentinean
Mexico --> Mexican
Columbia --> Columbian
Brazil --> Brazilian
Argentina --> Argentinean