My guess is the New York Rangers, they seem like the most likely candidate.
The Rangers finished off New Jersey Friday night with a 5-3 win, moving on to the second round.
Washington is down in their series 3-2 to Philadelphia, and Boston needs to keep their momentum up if they want to beat Montreal.
Boston fought back from a 3-1 series deficit to force Game Seven Monday night. The problem is they have to go to Montreal and come out with a victory to advance.
Boston has all of the momentum right now after winning a back-and-forth game tonight in Boston. But all could be for naught if they can't carry that momentum into Game Seven Monday night.
The Penguins should be well rested for any opponent after sweeping the Ottawa Senators in Round One.