I can find roll cages for 3rd gen cavaliers, does the same style cage work in a sunfire?
 
Probably, everything is the same but the rear quarter windows.
On the inside my car looks like a fighter jet.
 
 
if you are looking at an autopower roll bar, i have seen it mounted in a sunfire and can assure you it will fit.  their full bolt in cage may be another story as the dashes are shaped differently between the two and I personally have never seen a j-body running their bolt in cage.  I'm not sure how much clearance they allow for the dash.
That being said, if you are serious about caging the car, I would look into having a shop build a custom cage for your car.  you'll get better fit and more protection out of a welded in cage.
 
 
That's funny... The op said he could find cavalier cage kits all day long.  He asked about fitment in a sunfire 
 
 
What about a 4-door 99 ? it all looks like 2-doors roll cages.
 
 
Akira Legacy wrote:What about a 4-door 99 ? it all looks like 2-doors roll cages.
autopower has a listing for both roll bars and cage kits for the sedan j-body.