If the state lasts for enough and there is a clear ideological difference between Manchukuo and the rest of mainland China, the population could certainly develop an identity around the Manchurian state. East
Germany had no ethnic difference from West Germany and it was also established as the client of a foreign power, but there are still former East Germans who have some bizarre rose-tinted nostalgia for the communist era.
If there is some kind of language reform that makes the Manchurian spoken dialect of Han Chinese distinct from the rest of China, or a major divergence between Manchukuo's writing system and the rest of China, this could strengthen a Manchukuo identity. There might be a split over simplified vs. traditional characters, a new Manchurian writing system, or the adoption of some Japanese characters. The Manchurian language does have its own alphabet, but I don't know if that could be adapted to spoken Mandarin easily.
Meme-ing a national identity into existence is extremely difficult, but it's not impossible with some pre-existing distinction that can be emphasized and copious amounts of historical revisionism.