The math minor fits well with both Electrical Engineering and Computer Engineering. Depending on how early you make the choice to add a math minor, you can double-count most of the credits with other requirements that you would need to fulfill anyway.
Below are some guides to show you where courses will double-count and what amount of extra work you may need to do. In summary:
Electrical Engineers: With careful planning ahead, you can fit the entire minor into your program. This does not apply to everyone, though – check your personal situation carefully! You may need to take up to two additional courses (6 credits) beyond your degree requirements.
Computer Engineers: With careful planning ahead, you can fit almost the entire minor into your program. If you plan well, you can use one of the two extra courses as your Math/Science elective, leaving just one course above-and-beyond your requirements. This does not apply to everyone, though – check your personal situation carefully!
Math Minor Requirements (EE)
Math Minor Requirements (CpE)