IGN reports that Link will be only Right-handed in the Wii version of Twilight Princess. He will, however, be left-handed in the GCN version. Apparently, Link was going to be lefty in the Wii version, but Nintendo assumes there are more right-handed gamers than left-handed. IGN reports Shigeru Miyamoto confirmed all of this in a Q&A session today.
Update: Nintendo of America, Inc. will not be issuing an official statement about this, it will be revealed through natural game coverage and upcoming previews on websites and magazines. However, a very, very reliable Nintendo source has just confirmed to me that Link will only be right-handed in the Wii version - the early report was pre-mature and I'm not gonna name a name to protect that person's identify, but this is the first "wrong" info I've ever gotten...but oh well. To clarify, Nintendo of America sources, and Shigeru Miyamoto, have confirmed that Link is only right-handed in the Wii version.
So, sorry lefties. Now another reason for players to want the GCN version even more.