Seanie loves superheroes. Specifically, he loves the Flash.
I love Seanie, and I want him to be happy, so I would give him a superpower. But I'm not going to give him superspeed or whatever the Flash's powers are. I don't think I'd really benefit from Seanie running really fast. Sure, it'd be pretty cool if every time I wanted a snack, he could run and get it so quickly that it would almost instantly appear at my side. But I don't think Seanie would use his superpower that way; he'd always decline because he was "too tired" or "you'll get fat".
Flight would have the same problem. If Seanie could fly, would he give me a ride? Maybe. But he wouldn't carry me very far, and he'd probably drop me, so again, I don't think I'd really benefit.
Invisibility would just be a mistake. I would hope that he wouldn't use that skill to follow me around, but who knows? If he had the ability to do so, I bet Seanie would...not always, just once in a while. And I'd never know when he was following to class to make sure I paid attention, or sitting next to me while I read a book and following over my shoulder. Too creepy.
So I think I'll just give Sean the weird magnetic powers that Magneto has. That way, he can retrieve my ring if I drop it down the drain, get coins out from the couch cushions, and cheat at panning gold. If he decides to crazy and take over the world, he'll have the destructive power to take out the Golden Gate Bridge. It'll be cool.