Peter, I am Thomas Guerena. Luis is my father's cousin. My father is Mario Guerena. My grandfather is Carlos Guerena. Carlos was born in Alamos, Sonora as has been mentioned.
Yes, I believe it is true that the name originates in the Basque territory as you suggest. I am not aware of it having any Sephardic origins. A Google search of sephardic names did not yield Guerena within the list. I would be interested if you are aware of such origins.