Wrt Waterloo, they’re used to the specific subset of very gifted math/CS students who aren’t interested in much else. I understand your son isn’t “not interested” but “unable”, but the situation at Waterloo means their requirements are adapted to their subset and it should be easy to find classes with all multiple-choice tests in a non-CS/non math class or interesting topics that’d accomodate his needs. My assumption here is that he can read/understand fine, but can’t express his thoughts in a written paragraph.
UBC doesn’t seem to require much in Humanities from its STEM majors.
Less certain: Acadia, Lethbridge, Trent, Wilfried Laurier, Simon Fraser ; UOIT?; Bishop’s and Concordia should both have no general education requirements although they may have “correlate” subjects.
Truly the most specialized universities will be British, although Scottish and Irish universities will be somewhat more general but only in the sense they may require a related subject to CS vs. CS-only.
He’ll need a 5 on Calculus BC or community college calculus + two other subjects with a 5 (AP CS A not necessary but can be helpful)
Look into Imperial, St Andrews, Durham, Edimburgh, Bristol, Warwick, Glasgow, Queen’s Belfast, Cardiff (all UCAS, pick one from the last 2 for a “safety”).
CAO: Trinity Dublin (any “level 7” or “level 8” program in CS would also work).