The reason the Japanese didn't intend to resurrect the Qing is that it had lost all popular support from the majority Han population. This is why, with the Wang Jingwei government etc, they tried to co-opt the rhetoric and imagery of the Xinhai revolution, rather than the Qing dynasty.
Resurrecting the Qing would indicate rule by foreigners, which is exactly what the Japanese didn't want to do (although it was very obvious to everyone that the Greater East Asian Co-Prosperity Sphere was a massive sham).
They propped up Pu-Yi in Manchuria to win over the local Manchu population, which had recently been largely disenfranchised by an influx of Han Chinese during the latter years of the Qing and the Xinhai revolution period (prior to that, Han hadn't been allowed to migrate to Dongbei). The process of Han migration had been accelerated by things such as the construction of Harbin and the South Manchuria railway. Pu-Yi was intended to bring the Manchu over to the Japanese side. The more ethnic separatism the Japanese could encourage, the more they could sideline the massive Han ethnic group and make them easier to subjugate. Hence why they also supported the Mengjiang government in Inner Mongolia and Suiyuan (sp?) , which was nominally Mongol, but where over 50% of the population was Han. Incidentally, the Han population of those areas is now in the 90+% range.