Your pre req classes will give you the foundations you need, but most successful med students add specific MCAT prep on their own too - regardless of major. Choose a major you like. Acceptance rates are fairly similar across majors. If you like your classes, you’re more likely to do well.
Be sure you also have a Plan B you like. Only about 40% who apply to med school get accepted, even some with top grades and stats. Many opt for their major based on Plan B.