"Margaret Atwood is indeed Canadian."

Sure.
And the OP also specified novels *about* the US (of America) including fantasy. But I think most posters have forgotten that.

Atwood's novel is a dystopian vision of a near future, set somewhere in what once was the USA - in particular we imagine it must be somewhere in the bible belt. It fits the OP's request for: "books that get to the heart of the American dream, the American nightmare, the soul of the people and the essence of the country. ... I'm interested in anything ... From the wild west to the wildest flights of fantasy, the light and the dark, within and without,"

Wiki:
"The Handmaid's Tale is set in the near future in the Republic of Gilead, a country formed within the borders of what was formerly the United States of America. It was founded by a racist, male chauvinist, nativist, theocratic-organized military coup as an ideologically-driven response to the pervasive ecological, physical and social degradation of the country. Beginning with a staged terrorist attack (blamed on Muslim terrorists) that kills the President, a movement calling itself the "Sons of Jacob" launched a revolution under the pretext of restoring order, ousting Congress, suspending the U.S. Constitution. Given electronic banking they were quickly able to freeze the assets of all women and other "undesirables" in the country, stripping their rights away. The new theocratic military dictatorship, styled "The Republic of Gilead", moved quickly to consolidate its power and reorganize society along a new militarized, hierarchical, compulsorily-Christian regime of Old Testament-inspired social and religious orthodoxy among its newly-created social classes."

I think that fits the remit quite well.