well, last year I tried to book before EMH (September) and was told CP opens at 8:00 a.m., no change for breakfast hours on EMH day. Even the monorail resort table service places like Kona Cafe & Grand Floridian Cafe do not open until 7:30.
If you're wanting a breakfast before morning EMH, your resort food court is probably the best bet (counter service).
If you really want the character breakfast experience on an EMH day, try booking the latest breakfast seating (10:30 or 11:00) That way, if you grab a light breakfast like a cereal bar, and you can get to the park for early EMH, you'll get a wonderful 2 hours of park fun & then have a nice sit-down.