Who do the Vikings bring as QB2?

It seems obvious that the Vikings are confident in JJ McCarthy as the QB of the future. But we obviously need a backup/bridge/mentor QB in case he isn't fully healed, and to not rush his development (as stated by KOC). Who do you think we bring in, and who do you want?

Personally, I would love Joe Flacco. He has experience, he's a super bowl MVP, he's been around a few different teams, and he's also not against being a backup/mentor. He can still play, and while he can start, he's not going to be in competition to take the QB1 job.

EDIT: Totally forgot about KOCs pet project to "fix" QBs, like Darnold and Daniel Jones. I could definitely see them picking up Mac Jones as a reclamation project.