The re-release was suggested by a recent ESRB listing for a Wii U version of Super Mario Galaxy. Owners of the Wii original, which launched in November 2007, have always been able to play it on Wii U via backward compatibility.
Super Mario Galaxy will be available for Wii U through the system's Virtual Console. That's different from its sequel, 2010's Super Mario Galaxy 2, which was ported over as a native Wii U title and released on the Nintendo eShop this past January. That port also costs $19.99.
Wii U Virtual Console games support some of the Wii U's built-in features, such as off-TV play on the GamePad. However, the Wii U port of Super Mario Galaxy 2 requires a Wii Remote and Nunchuk, just like the original game did, so it's unclear if the Virtual Console version of Super Mario Galaxy will work with the GamePad alone. We've reached out to Nintendo for more details, and will update this article with any information we receive.