[quote=So Boerd]
You way overestimate China and Japan. The Russian Far East is the finest territory for guerilla operations in the whole world. Invading and defeating Russia from the east is impossible.
[/quote]
Guerrilla operations loyal to the Russian Empire, though? Russia had a nasty habit of exiling people disloyal to it to Siberia, and combined with the native population, I don't think there are that many pro-Russian Empire inhabitants, at least not enough to make a meaningful difference.

[quote=So Boerd]
They live there. It will be like the Boer wars but 100,000 times worse.
[/quote]
No it won't because China isn't invading Siberia in a war of conquest. They're waging war against Russia for Manchurian-populated lands in the East.

It would make more sense for guerrillas to side against the Russian Empire, all things considered, e.g. Russia's crippling debt, the large number of exiles and political opponents, the number of people who aren't of Russian descent, etc, etc.

[quote=NarcolepticSailor]
Basically this. I don't think that China or Japan can do anything else aside from having taken Vladivostok. I mean, are they going to force march through Siberia? They'd basically kill their soldiers so they can say they have control of basically nothing.
[/quote]
That's more or less all there is in East Russia except to sweep the provinces along the Sino-Russian border and put holes in whatever progress Russia made in the Trans-Siberian Railway which, btw, runs along this border to Vladivostok.

Actually invading Siberia isn't necessary. Any armies that are moving through the region are more numerous in population than entire regions.