I’ve disliked nearly every modern book on Emunah that I could find and read. They almost invariably try to “prove” that the Torah is emesdik using what is mostly junk science. The problem with that approach is that as soon as someone comes up with a way to invalidate that science or logic, the Emunah goes pop!
Emunah comes from within. The only way to strengthen ones Emunah are through personal actions and thoughts. If one is having difficulty with that, speak with a Rebbi or teacher as he/she will be infinitely more helpful than a simple book.