When they have a healthy squad I'm assuming from what I hear their D pairings should be;
Chabot-Karlsson
Phaneuf-Ceci
Oduya- Wideman
Borowiecki
So giving up a top 4 guy, would probably be Claesson, not Ceci. Ceci is from the area and that's a big draw for a team hurting to put people in the seats. No way they give him up. And that second turns into a first round pick and another defensive prospect and either Smith or Turris. Duchene probably comes with Commeau with half retained salary. And a second round pick? Close but I don't think you gave nearly the fair value that each team would need to let a trade like this go through. But I do see benefits for something like this to happen and I'm not a Sens fan but I really hope this does happen

Also Duchene would certainly be the number one center they have been craving for years since Spezza went. Not second line.

With the Sens wanting Chabot to play the right side, then Ceci does become tradeable. I would trade White, even before his injury, for the simple reason of burning that year on the entry level contract. Having two years to prove yourself and then coming up on the next deal so soon, make is difficult for the player and possibly expensive for the team. Chlapik is having a wonderful camp, and I would not want to loose him.
If the Sens are seriously considering this it must mean they think Chabot can play the right side and play in now. So hear are what I think the pairings will be:
Claesson - Karlsson
Phaneuf - Chabot
Oduya - Wideman
Boro