This is the closest Japanese proposal of what should be done to Siberia east of the Urals that I've seen,
I already asked this here last year, but other than mentions of occupying Soviet territory as far as Irktusk, making a demilitarized line west of lake Baikal, and putting Japanese settlers in Siberia while simultaneously having some sort of Russian self-rule, there's nothing clearly mentioning if Japan intended to set up a White Russian puppet state or annex the whole thing altogether after the war.
I understand that Axis objectives were inconsistent and plans changed as time went on, these two are from 1907 and 1926, and by 1942 there were radical changes, if some Japanese figures wanted to annex Siberia in the 1920s, then they would have probably had changed ideas by the time Kantokuen was being planned.
Anyone also has any sources if Japan intended to give the pre-1860 Outer Manchuria territory back to Manchukuo? since giving back stolen Manchu land would be a good propaganda move, the Black Dragon Society wished for Japan to annex territory east of the Amur River, North Sakhalin, and Kamchatka, so Manchukuo would've looked like this minus the space in red, perhaps only sources in Japanese mention this.