He should apply as the major he really wants. Note that if his desired major is more competitive for frosh admission, it will be more difficult to change into later.
What are his UC-recalculated GPAs (see https://rogerhub.com/uc-undergraduate-admissions-calculator/ ; most UC web sites use the weighted-capped version, and CSUs other than CPSLO use the weighted-capped version, while CPSLO uses a 9th-11th instead of 10th-11th GPA)?
CSU eligibility index (for other than CPSLO) = GPA * 800 + SATRW + SATM.
Some CSUs publish past admission thresholds: http://talk.collegeconfidential.com/california-state-university-general/2150136-csus-that-publish-past-admission-thresholds.html .
UC admission rates by GPA can be found at http://talk.collegeconfidential.com/university-california-general/2127392-faq-uc-historical-frosh-admit-rates-by-hs-gpa-2018.html . However, engineering majors should be considered more difficult than overall campus stats.