Given the above, Michigan is probably the most favorable to the student in terms of declaring/changing major, if he is admitted to the engineering division. But it can be much more expensive than UCs and CSUs for many California students (OP: have you compared net price calculator results?).
The UCs and CPSLO are favorable if he gets admitted to the major (some of them may admit some applicants to the school but not the major). However, if he may want to change to a different engineering major, those where the criteria to change are difficult (high GPA and/or highly competitive; this probably means UCLA and UCSD) are less favorable.
Purdue’s competitive system to enter one’s major does not look very favorable, though it depends on what the actual GPA thresholds are (which are not published on the web site).