3? More like 4! More might be said but I discuss the formation of the Japanese collaborator regimes in China proper in this answer, and their relationship to Manchukuo in this one.

To give a somewhat potted summary of the key takeaways, especially from the latter answer, Manchukuo and Mengkukuo were not conceived of as Japanese puppet regimes in China, but rather as breakaway regions under effective Japanese suzerainty. Japan's official foreign policy line on Manchukuo – insofar as there ever was one – ultimately sought to assert that it was legitimate as an independent state from China, as opposed to a Japanese foothold in China, derived at first from claims to it being a Manchu nation-state and latterly from claims to it being a state for a multinational 'Manchurian' identity. Neither was particularly convincing on the international stage, mind you, but it is worth suggesting that the former, at least, was not entirely spun from whole cloth – that most Manchus resided outside Manchuria and that Manchuria was mostly non-Manchu doesn't by default mean that the Manchus might not have been entitled to statehood had they desired it, and arguably Japan's foreign policy served to poison the well for that particular hope, had it ever been entertained seriously.