Are there any significant differences in applying to Comp Sci in the Engineering or Comp Sci + Statistics in the College of Liberal Arts?
The only application difference is that if you want any computer science major, in engineering or any of the CS majors in LAS that combine CS with another major such as statistics, you must list it as a first choice major in the application because you cannot list any CS major as a second choice.
UIUC does not provide actual admission rates to particular majors. What it does provide for many majors is the middle 50% ranges. You can search for that per major information on the site where you will find there is a little but not a large difference in the ranges for CS engineering and Satistics and CS, see https://myillini.illinois.edu/Programs/ComparePrograms (GPA shown there is unweighted)
Whatever you do, don’t apply to 1 as your first choice and the other as your second choice. They do not look at second choice majors for either CS or CS+X. The acceptance is so low you could end up with neither choice. This is from the admissions rep at the school when we toured this summer.
^You cannot make any CS major a second choice. If you want any CS major in engineering or LAS, you must make it the first choice. See https://admissions.illinois.edu/FAQ/applicant-freshman#second-choice-major and open “Are all majors available as a second choice.”