Qoolwater, welcome to the Dis!
If there is a place inside Epcot that holds particular significance to you or your future fiancé, then chose that location when you pop the question.
For example, if you always toss a penny into the fountain in France, consider stopping there and handing your future fiancé a penny. Ask her to make a wish. Once she has thrown the penny into the fountain and made her wish, you could pull the ring box out of your pocket and say something like, By any chance, did you wish to be my wife?
Or you could turn it around and toss your own penny into the fountain and make your own wish. Then you could say something like, I wished for you to be my wife. Do you think my wish will come true? When your future fiancé nods her head, you can get down on bended knee, pull the ring box out of your pocket, and pop the official question.
There are a million and one ways to ask someone to marry you. Search the Internet to come up with some really unique stories and then see if you can tailor them to Walt Disney World.
By the way, congratulations!