Settlement of the area won't really be possible until the Trans-Siberian Railway or equivalent is built, but that can be pretty easily circumvented if Russian surveyors stumble upon iron or coal deposits out there.
As far as effects, let's suppose that the discovery of Manchuria's resources causes the TSRW to be at least partially built 20 to 30 years earlier than OTL, to the effect that by the 1880s, there's a large settled Russian population there. Let's say that in the generation or so that Russia has held and settled Manchuria, industrialization has taken foot in the Russian Far East, particularly in the port city of Vladivostok. This is inevitably going to lead to a more cemented Russian naval presence in the Pacific, and probably with a few ships being built in V-stok.
Two major effects will happen here: One, China will experience at least a trickle of manufactured trade goods from the factories popping up in *Manchuria, and two, Japan will feel significantly more threatened by Russia.
If more goods and merchants are visiting China ITTL, anti-Western sentiments will run higher, maybe resulting an earlier or more destructive Boxer Rebellion. Japan and Russia will come into conflict over China (as OTL) earlier ITTL, not to mention more directly, since Russia now shares a border with Korea.
This could yield some interesting butterflies about Japan's development as a world power during the Meiji period. Maybe they focus elsewhere to avoid conflict with a beefed up Russian Far East? Or maybe they get stuck in a series of costly land wars in Korea and never reach their potential as a power. Either way, East Asia's political scene will be quite different.