Is there any reason the Russians couldn't be included too? Have them show up on the West coast and settle from Alaska down to Northern California. Also Belgium, Scandinavia and Germany would be fun. Not historically 100% accurate, but it's a big continent and the more the merrier. Oh, and the Incas and Aztecs should be regional powers. They have much more in common with the Europeans than with, say, the Tupis. Making them playable would be nice, too.