I attended American universities (as an American) and if he is good in a lot of disciplines, and is actually quite good in physics and computer science, the US approach will give him time to combine interests. Physics or comp sci would be a great BS, and then he could minor in something else like History to balance it out. Or double major (BS and a BA) if he wishes. I dont think the math weakness is really THAT glaring an issue if hes good at the other two, and general courses in both will allow him to find his path to what he really wants to do as there are so many sub specialties in each field.
You may want to get to grips with how the US university systems are arranged. There are the big state universities, some of which are very well-ranked globally (Michigan, North Carolina, etc) but have tens of thousands of students (and the research opportunities funding and labs to match). There are the private schools like most of the Ivy League, MIT, USC, Stanford, CalTech, to name a few. Some states have more than one university system (U of California San Diego is different from San Diego State and University of San Diego, for example). And then there are the super niche liberal arts schools (Smith, Wellesley, etc) and the religion-focused (BYU, Oral Roberts, etc).
What sort of environment would he thrive in? Does he like to join activities and social groups? Like big time competitive sports? Want a smaller campus feel with more individual attention? East coast, west coast, middle? Some are near the beach, some are near ski resorts, some are on beautiful lakes, some are in cities.
A lot of American kids go on university tours in their second or third year of high school to check out specific campuses, and the schools usually pull out all the stops to make sure those visits are welcoming - dorm overnights, college games, sitting in on a lecture, visiting specific departments of interest, meeting other prospective applicants, etc. Could that be an option if you are still unsure?
There really is no harm in picking reach, assured, safety schools and putting in some applications, especially if he does well on multiple choice (although I would highly recommend getting and SAT specific study book because there are certain strategies you need to know to be able to top out your score). He could very well get some excellent offers from some excellent schools in some incredible environments for opportunity.