With the Sens signing Nick Cousins I think it is pretty unlikely that they sign any current NHL forwards to a PTO. Maybe they do that for defense though.
I think there is an outside chance that the Sens offer some PTOs to some players that might earn 2 way contracts. Some of the currently unsigned players that seem to fit the Sens identity include Nick Ritchie, Brett Ritchie, Anthony Camara, Scott Kosmachuk and Luke Witkowski.
But like others on here have mentioned, these players could make more money playing in one of the non North American leagues than they will if they earned a 2 way contract.
The primary focus for the Sens, on the PTO front, is likely to shore up their depth on d. Those PTO options include: Jani Hakanpaa, John Klingberg, Anthony DeAngelo, Jared Tinordi, Marc Staal, Kevin Shattenkirk, Robert Bortuzzo, Justin Schultz, Tyson Barrie and Marco Scandella.