I wonder what ottawa would add to 3 oa to get there choice?
Ottawa certainly has a ton of picks to dangle. Last time there was a similar flip flop:
1998: San Jose traded #2 and #85 to Nashville for #3 and #29. It was the Preds first pick in franchise history, so they wanted a scoring forward to be the face of the franchise. Unfortunately for them, David Legwand's offense never quite took off. San Jose ended up with Brad Stuart and Jonathan Cheechoo.
1999: There was the overly complicated five team deal orchestrated by Brian Burke to secure both Sedins. Ended up being a bunch of swaps between picks for 3rd rounders, but everybody more or less ended up with their intended targets anyways.
2002: Interesting draft day swap as Columbus was paranoid that they would lose Rick Nash to Philadelphia who suddenly acquired the 4th overall pick (and apparently were talking with Atlanta for #2). Florida swapped #1 with Columbus for #3 and the right to swap 1st rounders in 2003. Florida then gave Atlanta a 3rd rounder to not pick Jay Bouwmeester (presumably matching what Philadelphia was offering).
2003: Florida had Nathan Horton at the top of their board, so they traded #1 and #73 to Pittsburgh for #3, #55, and Mikael Samuelsson.
2006: Boston offered #5 and #37 to Washington for #4, but the Capitals wouldn't do it after the Bruins rep told them they intended to take Nicklas Backstrom.
2012: Garth Snow channeled his inner Mike Dikta and offered his entire 2012 Draft (#4, #34, #65, #103, #125, #155, #185) to Columbus for #2. Columbus declined and took Ryan Murray.
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Realistically, might be too tough to trade down without the threat of somebody leapfrogging Ottawa (and the Kings willing to trade out of the top 3). Vancouver tried to get Vegas to swap #5 for #6 at the 2017 Draft, but Vegas was able to sniff out that Vancouver wasn't taking Cody Glass so they didn't make an offer.