Cornell vs UMich undergrad difficulty?

Especially in computer science.

I cannot answer to this specifically since I am not a student at either; however, I am not sure why this is even an issue. This is a subjective question and in a forum where unknown posters state their opinion, subjective opinion can be very misleading.
If you are looking for some statistics , I would suggest look at the mid range of scores for each university, look at their post-graduate job profile. You can also use govt college scorecard to compare the 2 universities. Then decide which will give you higher GPA - based on your own analysis. That’s the best I can suggest.

They are very comparable schools. Likely about the same.