Frankly, I'd be happy if we got a 7th for Burns, straight up. He's a lazy defenseman who doesn't play physically, doesn't skate like he should, has horrible defensive instincts, and generates more offense going the wrong way.
However, I don't think the league sees him that way, and I'm sure we could get something of real value for him. A 1st is almost certainly out of the question (maybe if we send a 3rd the other way and take a bad contract, we could finagle a very late 1st). I'd shoot for a 2nd from a team seeking the playoffs and take a bad contract, maybe retain a little bit. Burns can still generate some offense, and maybe you can shelter him if you have some actually good defensemen (the Sharks have no one who is legitimately good at defense).