You could maybe use it to get rid of Seabrook? Assuming he's willing to waive his NMC of course.
Obviously getting rid of Seabrook's contract would be good, but that's a waste of the 3rd overall pick. I know you'd be getting something else back, but still not a good think to do with a 3rd overall pick. Especially because Seabrook's contract is so bad that you're going to probably have to do 3OA+Seabrook for something like 10OA to 12OA + a prospect or something. I wouldn't try too hard to get rid of Seabrook's contract because the price will be too high. You can't just move Seabrook+2nd+extra prospect for a prospect of the same value as the one you're giving up. That's basically giving up a 2nd to get rid of Seabrook. Sure, that would be a good deal for Chicago, but a 2nd isn't enough to get another team to want to take his contract. Teams are going to ask for the 3rd overall pick. I don't see any way the Blackhawks trade that pick at all.
I think the reason teams never trade top 5 picks is a good one. It's because you have a chance to get a really good young player, so why not use it? I wouldn't go around offering it for a 25-29 year old defenseman. That just doesn't make sense to do when you can get a way younger player in the draft. And if you offer the pick for someone really young who's already in the NHL, if that player is good enough the other team probably won't take the deal.
The top 5 picks in the draft are all basically untouchable like most years. Those picks almost never get traded and I don't see why this year would be any different. But when I think about it, Detroit, Buffalo, Edmonton, Anaheim and Vancouver don't seem at all likely to trade their picks either. So, I think the top 10 are untouchable. Then I look at Philly and they're building a younger team who should probably just stay at 11 and make a pick. Then Minnesota kind of seems to be in a rebuild or retool. Even if they do decide to build for next year, that pick shouldn't be moved IMO. Florida's pick is the highest I could see being moved. I don't think they will trade it, but they could. If they decide they want to be in win-now mode, they might move it to acquire that last piece they need to be a playoff team next year. I could possibly see them doing that to build a better team for next year. I'm not sure though. All of these are guesses and I could turn out to be completely wrong.