Roussel is a good bottom liner and I like him in VAN and would like him in MTL, but he is overpaid and has not played a full season the last three years. It is hard to build a team with bottom liners making 3m in a flat cap world even more. VAN can do it because Boeser Horvat have good contracts in place, Markstrom has been playing like an elite goalie while ring paid like a 1B goalie, Pettersson and Hughes have ELCs and are performing tremendously. I don't think the same can be said about MTL (overpaid goalie and good youth but not elite like VAN)
So Roussel in himself does not hold a lot of value and the only interest of VAN to trade him would be to dump cap. Regarding Virtanen I believe he can be a good 3rd liner, does not seem to be a fit in VAN though, but I get why some fans don't want to trade him for a low return while he was 6 OA. Not sure he returns a 1st at this point though.