Square Enix uploaded a bunch of Kingdom Hearts 358/2 Days trailes on Japan’s Nintendo Channel. The videos aren’t new, but one clip shows characters outside of Organization XIII partnering with Roxas.
If you freeze frame the trailer at 4:45 you can see Donald and Goofy are playable characters (thanks for the tip Ricardo!!). This appears to be cut from multiplayer footage so it’s unclear if you can use either character in the story mode. The video also shows Sora in his bright red Kingdom Hearts 1 outfit bouncing around too. Whether Sora is playable or not is still up in the air.