This would be so cool! Alright, So I would have a log ride. Roller coasters are my favorite, but to actually have the feeling of the MLP theme, a log ride would be best.
When you enter, you would see (on both sides) the main six as fillies with Pinkie Pie Laugh song in the background.
Then you would travel through all of the ponies houses and see their pets, with Winter Wrap Up playing. After that you would see them getting ready for the grand galloping gala with all their dresses, and maybe scenes from canterlot. At The Gala song of course. Last I would introduce discord and have scenes where the main six each have their elements and fight off discord, ending with a rainbow.