Metroid - Never has been a big seller like Mario or Pokemon but i'd say it would sell a modest 1 to 2 million.
Pokemon Snap - Now a reboot of a cult classic which the gamepad is perfect for with the Pokemon name would move some uints.
Mario and Sonic Platformer Crossover - Would have to be done purely by Nintendo without Sega's involvement as they tend to make bad choices when it comes to Sonic.
Pokemon MMO - No comment as i am both apposed to the idea and against.