Super Mario Galaxy 2 was made for the Wii.
Nintendo released Super Mario Galaxy 2 in 2010 as a direct sequel to the 2007 Wii game Super Mario Galaxy. It was designed around the Wii's motion-sensitive Wii Remote and Nunchuk controls, while a second player could use another Wii Remote to assist Mario by collecting Star Bits and interacting with enemies.
The project began as an expanded version called Super Mario Galaxy More, but the development team kept adding new ideas until it became a full sequel. The finished game introduced new galaxies, additional power-ups, Yoshi, and a map system centered on Starship Mario.
The Wii U and Nintendo Switch can cause confusion because the game later became available through re-releases or enhanced collections. Those later versions do not change its original platform. Super Mario Galaxy 2 was developed and first released for Nintendo's Wii console, not the GameCube or Wii U.