Not sure who those PTO options could be but here are a list of some of the UFAs still on the market:
D-Men
PK Subban, Anton Stralman, Danny Dekeyser, Calvin De Haan, Ryan Murray, Scott Harrington, Kris Russell, Nathan Belaulieu, Keith Yandle, Ben Harpur, Zdeno Chara, Michael Stone,
Forwards
Brett Connolly, Antoine Roussel, Rocco Grimaldi, Zach Aston-Reese, Sonny Milano, Tyler Motte, Brandon Sutter, Evan Rodrigues, Brett Ritchie, Tyler Ennis, Sam Steel, Sam Gagner, Derek Brassard, Jimmy Vesey, Matthew Strome, Kole Sherwood, Alex Galchenyuk, Brian Boyle, Michael Dal Colle, James Neal, Evgeny Svechnikov, Zac Rinaldo,, Jonathan Dahlen, Daniel Sprong
On the back end it seems like a lot of those players could be options.
Up front, given the Sens style of play and the fact that the openings would be for bottom six forward roles, I could see Roussel, Ritchie or Neal being options. Ennis has the Sens connection so he could be an option. Galchenyuk and Sherwood had a stint with the Sens organization so I am not sure if they would want to give them another look. Dal Colle has the DJ Smith connection. Then with Milano, Steel, Sprong and Svechnikov they are former high picks so they could be reclamation options but I am not sure if they are well suited for depth roles.