I think he was also supposed to play Matthew Broderick's character...
And looking up the IMDb trivia:
The late Chris Farley, Adam Sandler, Paul Giamatti, the late Phil Hartman and the late Robin Williams were considered for the role of the Cable Guy before Jim Carrey was cast.
While filming of the scene in which The Cable Guy plays basketball, it became obvious that Jim Carrey could barely dribble a basketball, nevermind make a basket. Ben Stiller had Carrey mime the action without a ball, and VFX added the basketball in post-production.
Ah i love the IMDb trivia section