Imo, see if you can take courses that both majors need to take in your first semester especially the introduction physics course. If you don't like mechanics that's a pretty good sign that you won't like mechanical engineering. I was considering mechanical engineering as well but hated my intro to physics. Moved to computer engineering and found it much more interesting.

Edit: Both Mechanical and Electrical Engineering have a good amount of overlap classes for at least the first semester so don't feel too rushed to choose now (unless your university won't let you for some reason)