Lets think about who Cody is aligned with and who his options are as a replacement. Amber and Jocasta won the Battle of the Block therefore they can not be renominated. They would have been the best options to nominate opposite Brittany guaranteeing someone who would nominate Cody and his allies would be leaving. Derrick is Cody’s strongest ally he is not going up. Christine, Frankie, and Zack are his next strongest allies and not an option for replacement. Hayden along with Nicole are also allies probably not options. That leaves just two viable options Donny and Caleb.
Donny is well liked by everyone in the house but not exactly trusted. He's secretly aligned with Derrick and Frankie in Team America. Jocasta is a solid ally of Donny as well. If he gets nominated against Brittany he probably stays. If they decided they want Brittany gone, and it looks like that, this will be their play.
But what if they want to make another power move and get Caleb out? Here is how I would do it. First you tell him if Donny goes up Brittany stays and she will be coming after them. That means one of us has to go up. Then you build up Caleb’s ego saying he is the only one mentally strong enough to not crack under the pressure of the block. Tell him to imagine Zack or Frankie up there. There is also the added benefit out keeping Brittany quite thinking she is safe now. Tell him he will not go home over her because they have the votes. You say we had you last week we will have you again. Will he buy this? I think he might but even if he does not he can't stop you.
Why do I think this the best plan? Well you can get out two people this week.
Caleb - A huge physical threat who is an ally now but becoming more unhinged everyday.
Brittany - A paranoid loner in the house who you finally might be able to convince you have her back after saving her a second time.