This comes from the Iwata Asks interview...

Golf
The ball is displayed on the Wii U GamePad screen by your feet, and the fairway is on the TV screen ahead of you. You can play just like you would play as if it was real golf. This time, if you face the Wii Remote Plus toward the Wii U GamePad by your feet, the head of the club appears on the screen. And if you twist the Wii Remote Plus controller, the club head turns, too. Then, if you hit in that position, you can hit a fade and so forth. Golf will be ready for people to hit the green with it soon.

Baseball
As for Baseball, the basic control is swinging the Wii Remote Plus like a bat. The pitcher uses the Wii U GamePad. You look into the Wii U GamePad and choose a course and type of pitch and throw. You can enjoy trying to outfox the batter.

Boxing
For Boxing, they are considering a lot with regard to network compatibility and so on. Have to wait a little longer for that.

Source: Iwata Asks