Didn't realize goaltender was such a need. A lot is going to depend on the health of Matt Murray and how much faith the team has in a) his ability to remain healthy and b) the depth at that position.
At face value though, the Sens were likely going to carry 3 goaltenders next season, so moving a cheap guy like Gustavsson (with upside) could make sense as part of the deal. Would surely be more than #7 + Gus, but it sounds like that could be an easy way for Ottawa to add a bit of value.
The Senators also have a bunch of B/B+ winger prospects who I'm sure they'd have no problem including (Jarventie, Sokolov, Boucher?, Ostapchuk, Lodin) along with a couple of (relatively) high end RHD prospects (Thomson/Bernard-Docker).
Still feels like the Devils are the biggest threat to a Fiala to Ottawa deal. I doubt the Sens could compete if they put #2 and/or Holtz on the block, but beyond them I think the Sens may be the best fit to give Guerin what he's looking for.