There are no guarantees, no matter how many times you try to rephrase the question. No one on this website can guarantee that you will receive better chances with any specific major.
UCLA is a reach for everyone.
The UC’s are good schools. If you can get in, you’ll receive a good education.
(Oh, and if you’re trying for the med school, the UC’s aren’t the best place to do undergrad. Competition is fierce. Classes are large.)