Hard to say, but have the Canadians not solved it? They must have some generic term for the people in the next country.
The term American to refer to residents of USA has been in use at least 200 years, and is universally understood. In a sense it is easy to understand why. USA was the original independent nation in the Americas and thus had first digs on the term; secondly USAers or US Americans is a bit of a mouthful to use for a simple description. The nationals of the 3 North American countries are routinely described as Canadian, American and Mexican, even official treaties and documents use this terminology. Though Canadians technically are American, I have never heard this used by anyone in my lifetime; Canadians are very often mistaken for (US) Americans and called that, but they great umbrage at the practice. So in N America at least, there is no ambiguity as to who "America" refers to.
I cannot speak for S America, but I believe that residents there are also very clear as to who "Americans" refer to. Thus the terms Bolivians, Brazilians, and Americans are easily understood.
Even in motor sport terms, which concerns us here, there are plenty of examples of usage:
The original Can-Am series was run in just Canada and USA. It was thankfully not called the Can-USA series.
Dan Gurney's AAR team used the 2nd A for "American", his emblem was based on the US flag.
SCCA and ALMS series
Language evolves over time and common usage becomes dominant; that I believe is the case with the term 'American"
Edited by D28, 01 March 2015 - 19:48.