McCain or Giuliani may not run on a pro-gun control platform, but their previous record on that issue will follow them around like a dog after a bitch in heat. Giluiani's record on that issue in NYC is as bad as Hillary's or any other Democrat's, and McCain showed his true anti-gun colors right after the Columbine shooting. Add Giuliani's NYC position on 2nd A issues to his outspoken support for abortion and homosexual "rights", and he would lose every state south of the Mason Dixon line and most of the interior western states to boot.
As for the Democrat nominee he or she would have to denounce the party platform's position in order to appear to be against more gun control laws, and even then that wouldn't fool anybody who hasn't lived in a cave in Borneo for the last 50 years.
If you think about, the average Southern RATs (at least on a local level) are more conservative than Rudy McRomney. It goes to show how the GOP lowered its standards. Roy Barnes and Zell Miller would make better Presidents than the GOP frontrunners.