Hi David and 
bienvenue to planDisney!
Congratulations on your upcoming engagement and thanks so much for stopping by today with your super important question.
First of all, let me say that I cannot think of a more magical place to pop the question than right in front of the iconic 
Sleeping Beauty Castle at 
Disneyland Park and on Christmas Eve, no less! It's certainly going to be a proposal to remember!
Might I suggest first of all, that you get in touch with 
Disney's Fairytale Weddings to see if they are able to offer something along the lines that you are looking for. You can contact their team of Wedding Planners by emailing: weddings@disneylandparis.com.
If you would prefer something a little more low-key, another idea would be to stop by the cart that sells champagne in souvenir flutes on Main Street U.S.A. and propose whilst raising a glass, during, or after, 
Disney Tales of Magic. 
Top Tip - The majority of the crowds tend to disperse pretty quickly once the nighttime spectacular has finished so, if you wait a little while, you should be able to get some lovely photos, in front of the castle, to commemorate the special occasion.
Wishing you, your very own, Happily Ever After!
Emma