Roy is a very smart and strong player and quite good at maintaining possession. He'd pair well with Slaf and Dach for this reason, but I don't see this line happening at all. He's great at using the strengths of possession demons, even those with lesser offence awareness and make them better players. He would have been absolutely deadly with the Danault and Gallagher of years past if the ages had matched; I think he would have flirted with PPG
He's a bit of a headache in the lineup currently, I think he has a slightly higher offensive ceiling than Newhook, but the latter is much faster and is a left shot C/W hybrid who's further along his development curve. Newhook is the ideal partner for Dach as he became quite decent on the faceoffs (a notorious weakness of Dach) last season. I think barring a terrible showing from Newhook or an extraordinary one from Roy in the pre-season, the former will complete the 2nd line and Roy will play on the 3rd line. He's way too good to play on the 4th line though
I'd love him with Armia on the 3rd along with Dvorak. If Dvorak is finally healthy and plays for his last big contract, this could be an excellent 3rd line. Gallagher could do well instead of Armia here too if the latter struggles or is injured.
Roy should also definitely see some PP time. I'd love to see a 2nd wave of Laine or Caufield - Roy - Hutson, Guhle, Barron or Xhekaj - Dach - Dvorak.