Skriniar is right footed, so would make more sense if we feel he could partner Laporte. He will cost Maguire level money (if not record breaking), so I can't see us signing him as anything other than a partner for Laporte, or we are looking to go 3atb long term.
I don't know anything about Matviienko, but he's left footed, so I can't see him being an option to partner Laporte and would be viewed as a backup. He's also shorter than Garcia and whilst we have seen that height isn't hugely imperative with the recent Fernandinho/Garcia pairings, I do feel we could do with another big bastard to give us some more aerial presence.