A few little nuggets of information, from my experience with Carls:
5A is a pretty reliable anti-air in this match up, it will stuff any of Carl's air dashes aimed below your neck; you're out of luck if he's air dashing at your head. 5A will also lose to his dives.
If you find yourself caught between Carl and Nirvana, which you inevitably will, IB is your best friend. A good Carl knows you're looking to Sledge through Nirvana and hit him, so he'll try and bait it. IB during big gaps in his strings, then jump or back dash away. You can try hitting him with 5A and begin pressure, but make sure to mix it up because he can IB predictable strings and CH you.
If you Sledge Nirvana, you can mash 5A to lock her down in a ridiculous looking combo. This will cause your audience to laugh uproariously, demoralizing your opponent. You can contribute by saying things like, "Yeah, take it bitch, you know you like it" to heighten the effect. Forget what you've heard, this is the real tournament metagame. Spamming 5A after Sledging Nirvana will do a lot damage, depending on how long you can get away with it. If he air dashes at you, you'll stuff him and you might CH one of his pokes if you're lucky.