If you are having GMF when EMH isn't on in the morning, you will get into Fantasyland earlier than 10am, as thats usually where the GMF breakfast is taken (but not always). As has been said already, you will be told when you check in which restaurant in the Park is doing your GMF.
However, the rides in Fantasyland don't open until 10am if there is no morning EMH, so you won't be able to ride them until then. You can be first in the queue though - very handy for Dumbo! (we did Dumbo twice, the teacups and the carousel without any real waiting thanks to our GMF in Fantasyland in February).
If EMH is on in the morning and you want GMF breakfast as well, from what I understand you can't have GMF until at least 8am (when EMH starts), but what we intend doing is being at the Park for 8am to do some of our favourite rides in Fantasyland (and Buzz of course) and then taking a late slot for our GMF breakfast (ie 9.30 or 9.45).
Elaine