What are the consequences of Manchurian Controlled Eastern Siberia during 1400's, What if the Manchus conquered Eastern Siberia including Kamchatka Chukotka Peninsula what will happen? Will they discover America?
Having investigated the Manchu, I don't think that they were in a position to do that, especially as they didn't exist as an actual nation, well, an actual state, during that period, but rather several confederacies of tribes.
A migration would be needed, or a great population boom for starters.
A Manchurian unification as the one achieved by Nurhaci in the late 1500s and early 1600s might also be a requirement.