Make Russia and/or USA Colonial Empires rather than land Empires. Bonus points if the American west is native American/black majority. POD’s no earlier than 1776
The issue with Russia is that everything in it's physical existence points toward land expansion. I guess you could have it conquer parts of Southeast Asia and China, while forcing Japan to give it its ports for military use.
I meant more in the Empires Structure rather than a geographical change
That's still problematic. The American West and the Russian Far East are very thinly populated, and the inhabitants at the time are largely nomadic and not exactly acquiescent to the demands of American/Russian interlopers. If the Americans and Russians want a return out of their conquered territories, they need people in them. The best option is to flood them with their own settlers, as they did OTL, or those territories are going to sit there producing nothing of value for their respective owners.
Your idea in the first post of a black majority in the OTL Western US is intriguing, though. I suppose one could change some event early in US history to have slavery more entrenched, and then have the west settled by small communities of white "lords" and their more numerous black "serfs", to use medieval terminology. Maybe Amerindian peoples are rounded up to use as additional labour in constructing forts/mining operations/cash crop plantations, etc... (wow, this scenario is getting even more depressing than OTL...).
Of course, given the emergence of Manifest Destiny, that course of action is rather unlikely. For Russia, I don't think something similar in Siberia is even remotely feasible.
Alternatively, the USA could ignore overland expansion (though the question remains: WHY?) in favour of mucking around in the Caribbean and Latin America even more than in OTL. That would establish it as a coastal nation with a colonial empire scavenged from the remains of older European possessions (most likely Spanish ones). It's not a stretch to have it jump into African colonialism from there.