Hmmm hard to say, hard to say.
Well, when does all this colonization go about?
On the off hand I could see the two to definitly have some sort of colonization to be China and Japan, but still they are tricky.
First China, if this is Ming or later China (they did throw off the Mongols) I would imagine they would be in the best position to colonize. Due to their:
1.Might
2.Population
3.Technology
Yet, they would make the MesoAmerican Nation-States protectorates (they had a heganomic empire) but maybe little "China-Towns" on the coastal areas for trade.
On the Californian coast I can definitly see as a main area of colonization-filling around silver/gold lodes and the fertile areas and non-fertile (the Chinese irrigation and canal systems were superior to all untill the Industrial Age) lands bringing life much as it is now.
Japan: Depends if it unified or not, but colonization possibles are able for both.
Japan having a large-large-large pirate population. I can see independent Pirate-Lords setting up towns that grow into pirate strongholds up and down the West North American coast (preying on Chinese shipping).
My thoughts for the night.