Well the cap space is a huge factor in this. Ottawa wants to get rid of Ryan; Tampa needs to get rid of Callahan for Karlsson, likely Johnson and Killorn to resign Kucherov.
The Rangers don't have any critical piece up for a massive extension except Kreider in two years. Skjei too if he has a huge year or two that will cost UFA years.
Tampa has enough assets to please both Ottawa and the Rangers. Foote, Katchouk, Raddysh, Cirelli, Sergachev are their best prospects. Ottawa has several blue chippers but they dealt away Bowers and their 2019 first for Duchene, so it's doubtful they will part with anyone south of 22. I think they woukd rather eat Ryan's deal than move another prospect.
I think taking on Callahan should cost Tampa Sergachev, but Ottawa likely wants him too. Yzerman in 3-4 years won't be able to afford him anyway.
I'd be fine with Foote and Lipanov, or a 2020 1st and Raddysh or Katchouk.