If Spike’s Tails, Twilight would be Sonic then Rainbow being him and Twilight being Sally. Even though Sal and Twi are princesses, Twilight wasn’t a princess when she was born. Sally was born as a princess.
Applejack as Bunnie makes sense cause they’re both western. I see AJ as Knuckles more than Bunnie because both are very strong.
I see Rainbow as Shadow then Sonic because RD claims to be the fastest when she isn’t too me and Shadow claims to be the Ultimate Life Form. Both are stubborn, cocky, reckless (Mostly RD) and have an ego.
Pinkie as Amy is acceptable. I would think on having Comet Trail as Amy. I’m sorry if I had to say it.
Flash Sentry as Sally would count since Sonic had a crush on Sally and Twilight had a crush on Flash (Support Flashlight fans).
Pinkie as Tangle will count since Beau Skunky made a good point since both are quite hyperactive and very friendly.
Fluttershy as Whisper is amazing. Since both are quite. Fluttershy is friends with her animals and Whisper has the Wisps as her only friends when the Diamond Cutters (I think that’s their name) died and Mimic betrayed them.
Rarity as Rouge is good but I see her as Silver more than Rouge. Her magic is the same color of Silver’s powers and I found that interesting
Spike as Tails is great since Spike is Twilight’s number one assistant and Twilight’s adopted little brother and Tails is Sonic’s sidekick, best friend and adopted little brother.
And finally, Twilight as Sonic since both are main characters. Twilight became a princess after fixing her friends’ cutie marks and Celestia made her an alicorn (I think it’s bullshit since now Twilight outlived her friends) and Sonic was a prince in Sonic Underground and he became the true King Arthur at the end of the game Sonic and the Black Knight. Both are willing to forgive and forget. Twilight forgave Sunset, Starlight, Discord and Trixie (I think) and Sonic forgave Merlina, Knuckles, Shadow and Silver.

@Background Pony #97B1  
Tangle isn’t quite as goofy, but she is quite hyperactive, and very friendly like her.
 
She has her Pinkie-like moments though.
 
 
(And for context, she’s refering to Sonic in a running wheel. Don’t be perv’y.)

I see pinkie as more of a tangle to be honest

This is super cool and I can see them cosplaying as these characters

@Xavior  
I guess Tangle fits too, (sense she’s a li’l hyperactive too) but then one of the others would have to be Amy, and none of ’em really fit her.

I would have made Pinkie Tangle, but cute art regardless.

@Background Pony #8BED  
Me too. Hehe actually, all these characters suit them.

I like spike as tails

I like how they mix characters from 3 different canons here.
 
@Shritistrang  
Whisper the wolf kinda suits her, because she’s a bit shy/quiet too.
 
@Vatobot17  
Or Shadow.

I would rather put Fluttershy as Cream, then again I never read the comics.

I’m guessing Sunset is Blaze?

Rarity looks very nice in that Rouge outfit!