"for Engineering you more-or-less need to be an elite math/science student (as in at/near top of your class and top test scores)"
I kind of agree but I have to clarify on some point - a good number of engineering students I know aren't that type of people - they are simply people who enjoy doing that kind of thing / wants to do that kind of thing for a career / has no idea what they're doing. It's just that the engineering school tends to attract students of the engineering archetype. In fact, one of the best ways to distinguish yourself in applying for the engineering school is showing that you have strengths and interests elsewhere too.
However, I do agree that if you want to do well once you get in, you should definitely be very solid in math and sciences.
"whereas for CAS top 10% across the board will generally qualify you. "
You definitely need to stand out in some way as you would need to for engineering (but in different ways). Being top 10% really just means that you're at the "passable", but you aren't going to get a good shot if you don't distinguish yourself another way. 93% of the admits are in their top 10% of their class, so it's more of a basic requirement than anything.
Anyway, looking from this, ENROLLING engineering students seem to have a higher math score, and enrolling arts students seem to have a comparable/ slightly higher reading score. Overall, engineering has a higher admission % than arts. I'd say it's comparable so just let the requirements/ your interests decide for you. http://dpb.cornell.edu/documents/1000003.pdf#zoom=100 http://dpb.cornell.edu/documents/1000176.pdf#zoom=100