Davenport, Myskina and venus are made for those roles.
Wouldn't Justine make a better boxer - obviously not heavyweight - though you never know? Wouldn't Serena's large breasts make a painful target- or would they serve as protective padding?
Elena D would probably be too tall as a gymnast? Jumper? Pole vaulter?
Kim on ice I can see.
Smashanova P in the marathon?
The sprint racers? Amanda, Francesca? Myskina?
Table Tennis? Patty?
I can't quite place Jennifer - wrestling keeps on coming to mind but thats a worse fantasy than Serena boxing