Fluttershy - Pod People: Fluttershy is very similar to Tommy, the film’s child protagonist, in that they both have an interest in animals. Yes, I can also see Fluttershy trying to raise an alien being whose relative ends up going on a killing spree.
 
Rainbow Dash - Space Mutiny: With all the action going on in this film (“We put our faith in Blast Hardcheese”), Rainbow Dash would very likely be a fan of this film.
 
Rarity - Design for Dreaming: A pair of hammy performers singing and dancing at an auto show + some fashion show elements during the second half of the short (with the models showcasing the cars) = Perfect title for Rarity.
 
Applejack - Gunslinger: The film is a Western about a widow who takes over her slain husband as sheriff of a Wild West town, something that would probably fit a cowgirl like AJ.
 
Twilight Sparkle - Quest of the Delta Knights: The film is a medieval tale about a young boy who, the subject of a prophecy, is trained to become a Delta Knight and sets out of a quest to find the lost storehouse of Archimedes. Like the hero, Twilight is trained to become one of the users of the Elements of Harmony and eventually embarks on a quest to find them.
 
Pinkie Pie - Mr. B Natural: Given how the short’s title character is a crazy being who is very much in a “sing song” mode and tends to pop out of nowhere (i.e. a kid’s locker room), associating this with Pinkie Pie is a no-brainer.
 
Celestia - Monster A-Go Go: All I’m saying is this: once you watch the film, you’ll know why I associated it with Celestia.