They'll go for Certain Affinity (negotiate a deal with current owner to sell), Avalanche (same), Crystal Dynamics (same), and IO Interactive (same). And MAYBE a Japanese developer/studio, but if not then they will try partnering with one (get Arc System Works to do an anime-styled Killer Instinct for example).
Realistically those are the only four studios I could see them getting so should this ABK deal 100% fall through, and it's already like 95% of the way there. Alongside that if they do get Crystal Dynamics I think they'd also try getting a license or purchase the rights to Tomb Raider and Hitman from Embracer, since the teams responsible for those would be moving from them to Microsoft.
Also notice the four studios I mentioned already have ongoing game development relationships with Microsoft. CA on Halo, CD on Perfect Dark reboot, IO Interactive supposedly working on a dragon-themed exclusive for them ATM, and Avalanche working on Contraband. That's why I said if they wanted a Japanese developer, it'd be more likely they do a partnership for an exclusive, rather than buying them outright (Arc Systems Work for example would probably create conflict with Bandai-Namco if purchased since they developed Dragon Ball FighterZ and there'll very likely be a sequel to that in the future).