Personally, I will bet on Stussy and another guy from CP-0.
Stussy knows the state of emergency in which Whole Cake Island is, given she was there when Luffy and cie raided the tea party.
And I think the World Government would have not been against retrieving Germa specimen like the Vinsmoke children to create clones with powers.
But I don't know if it makes sense chronologically speaking.