UIUC and Wisconsin are different in this respect. UIUC admits to engineering majors but its “weeder GPA” is only 2.25 in technical courses to be able to enroll in junior/senior level engineering courses: https://wiki.illinois.edu/wiki/display/ugadvise/Technical+GPA+Requirements . On the other hand, Wisconsin weeds much more aggressively, with some majors having “weeder GPA” as high as 3.5 in technical courses and 3.0 overall, and no engineering major having a “weeder GPA” lower than 2.8 in technical courses and 2.5 overall, in the most recent year listed (2016-2017) at https://www.engr.wisc.edu/academics/student-services/academic-advising/first-year-undergraduate-students/progression-requirements/ .
But the weedout policies is some midwestern flagships are probably not relevant to someone choosing between Grinnell and Middlebury.