A 1903 widely circulated pamphlet by the name of
The Revolutionary Army by Zou Rong called for the "annihilation of the five million and more of the furry and horned Manchu race." He also writes: "Unjust! Unjust! What is most unjust and bitter in China today is to have to put up with this inferior race of nomads with wolfish ambitions, these thievish Manchus, as our rulers."
In 1905 the leading revolutionary organisation Tongmenghui (Alliance) demanded the "expulsion of the Tartars", referring to the Manchu.
Seven main points against the Manchu seemed to be:
- They were alien, not "Chinese"
- They had been barbarous and heinous in their conquest and control over China.
- They had barbarised China with Manchu customs.
- They had set themselves up as a privileged minority.
- They had subjugated the Han in the manner of a foreign military occupation.
- They practiced political discrimination against the Hans.
- They were, on their end as well, fundamentally at odds and hostile with the Han people.
Until about 1905 or so the Han were forbidden from settling in Manchuria, effectively making it quite like a foreign country to the Han. When the restriction lifted Han Chinese from over-populated northern Chinese areas soon flooded in, perhaps how one would move into a colonial frontier.
From these I would infer that the Manchu were indeed quite disliked and at least once did I see a reference to slaughtering of Manchu people after the revolution with a mention that the revolution wasn't quite so bloodless as it is often portrayed as. No actual historical mentions were given at that point, however.
Still, I would wager to say that the status of Manchuria as Chinese core lands is quite disputed. The original populace was vilified by the Han, the lands themselves had been closed off for about 300 years as a colonial overlord's lands might be and the Republican revolution had relied heavily on the anti-Manchu sentiment. Such a reliance and sentiment can hardly be changed overnight by adopting a slogan of unification. It is very true that the loss of Manchuria to the invading Japanese forces were a source of anger and shame to the Chinese and resulted in resignations in the government for their incapability to resist or repulse the invaders. This, however, does not mean that the lands were considered a core area. In a similar vein military commanders and government officials have been held responsible for not holding the line in offensive wars turned defensive, the German invasion of Russia coming to mind first and foremost. The humiliation at not holding onto an area is not so much about the area but about the incapability to resist and win.
In short I would say that Manchuria is a complicated piece of land at the time.
Sources: Rhoads, E.J.: Manchus & Han - Ethnic Relations and Power in Late Qing and Early Republican China, 1861-1928; Wikipedia