Mexican vs Mexicano

Mexican and Mexicano both are nouns.

Word	Noun	Adjective	Verb	Adverb
Mexican	Yes	Yes	No	No
Mexicano	Yes	No	No	No

As nouns, Mexicano is a hyponym of Mexican; that is, Mexicano is a word with a more specific, narrower meaning than Mexican:

Mexican: a native or inhabitant of Mexico
Mexicano: a Mexican (or person of Mexican descent) living in the United States

Other hyponyms of Mexican include Taracahitian, Chicano, greaser, taco, wetback, Mexican-American.

Mexican (noun)	Mexicano (noun)
a native or inhabitant of Mexico	a Mexican (or person of Mexican descent) living in the United States

Mexican (adjective)	Mexicano (adjective)
of or relating to Mexico or its inhabitants