From IGN:
December 13, 2004 - Recent rumors circulating the Internet have alleged that the latest installment in EA's hit freestyle basketball series, NBA Street, would feature an all-new cast of Nintendo-style characters. And if a new piece of box art posted on retail sites is to be believed, the rumors are true.
The Nintendo All-Stars, or more specifically characters like Mario and Peach, are set to be playable characters in EA's forthcoming NBA Street V3 for GameCube -- at least, that's what we can gather from the included box art. This is definitely one unique way to distinguish the sports title on Nintendo's platform.