There really aren’t many RHD that are actually available right now unfortunately. Tanev, Savard, Fabbro, Carrier, Walker, and Lyubushkin seem like the names being thrown around. Given the asking price for Tanev and probably Savard, Fabbro seems like the next best option. I can see Tre going for Walker though if he’s looking at RHD specifically.
Just my opinion but - Tanev is a natural fit with Reilly.
Savard I think is past his expiration and hasn't played good hockey in a few years.
Carrier is good, but while he plays with a weak partner in Lauzon and would benefit from a move, he has never been the player to back up an attack first battery mate.
Same for Walker, he is good but no history of being the backstop for an offensive partner.
Fabbro plays beside Josi so he fits the role nicely but he might be less skilled than Walker or Carrier.
Bush had his version of a career year as a Leaf for 31 games and has never come back to that modest level. Third pairing only.
I pick Walker if he can be had for less than Tanev. He is paired with Seeler who is a stay at home pilon but his advanced stats are quite good, and get better away from Seeler beside York or Zamula who are a bit more offensive. He is 53% O zone faceoffs compared to 39% for Carrier so his shot based metrics are necessarily going to look better but Rielly is also 53% O zone.