My prediction on who the Penguins will protect:
7 forwards:
Crosby and Malkin are automatic because both have no movement clauses in their contracts (and presumably neither would be asked to waive that clause without the Pens getting something large in return from Seattle). Jake Guentzel has to be protected and I'd imagine so does Bryan Rust since both are on the first line with Crosby and both are also on the top power play. I think the next two are Jared McCann and Kasperi Kapanen. Both are young, fast, productive two way players. No reason to let either exposed here.
That leaves one of Jason Zucker, Brandon Tanev, Jeff Carter, Teddy Blueger and Zach Aston-Reese. I don't think Zucker gets protected because he'd be a high cap hit for the Kraken. Zach Aston-Reese is probably the least valuable of this group, so probably not him. Carter's better days are behind him, so I don't see why he'd get protected. Between Tanev and Blueger -- I don't want to lose either -- I'd probably protect Tanev. He's just so productive all over the ice. It's a different team with him out there. So those are my choices.
3 defensemen:
Letang has a no movement clause so he's protected. I'm assuming Brian Dumoulin also will get protected. As previously stated, Marino and Olivier-Joseph don't have to be protected. So that's four guys already.
Of Mike Matheson, Cody Ceci and Marcus Pettersson, the Pens need to choose one. I think I'd choose Ceci and hope Seattle takes one of the other two and free up cap space (both Matheson and Pettersson have $4 million + cap hits).
Goalie:
Tristan Jarry. Like or not, he's not being left unprotected.