He should probably apply to US universities where he can combine tech and French in addition to French “Écoles” (Polytech, above, is another one, a bit like a small Cal Poly).
To make this possible as a livable endeavor for an undergraduate, stay away from anything “Université” including the Sorbonne.
A good US college would be URI for its Engineering/Language programs. Lafayette would be accommodating. Brown too although it’s a reach for everyone. Georgia Tech has a French campus. I think Colby has a first-semester-in-France program.
The INSA, through the Global INSA programs, is a Grande École that welcomes international students and they have a campus, on-campus résidences, dedicated staff for internationals, a French language program, etc. with easy access to interesting cities. I included links knowing you have plenty of time to explore. X Bachelor, ESSEC/Centrale Data science, and GlobalINSA are all in English so should be the focus.
He could also simply go through AFS and spend a year in a French HS (for his interests: spé maths/maths expertes, spé NSI, ie., 9 hours of math, 6 hours of CS a week, then core curriculum of Philosophy, English, Spanish, History, Environmental science, Geography). From there he could apply to both French and American colleges.