The bottom pair will be fine. Kulak has always driven the 3rd pair to good results no matter who his D partner is.Last year, the top pair was the best top pair in the NHL, and the bottom pair was one of the best in the NHL as well. The 2nd pair wasn't good but the team was good enough around it so that it didn't do too much damage. This year, we can expect Ekholm-Bouchard to stay near the top, but simply put, we don't know what we have with the 2nd or 3rd pair. We also don't know how Nurse will look, seeing as he's still recovering from an injury he got in the playoffs. There's a lot of uncertainty there.
The biggest question, as always, is the 2nd pair. It was a big question mark the last 3 years and the same this upcoming season.