A lot of polls show Giuliani gaining ground and fast in traditionally democratic areas. I could almost assure you that a strong Giuliani campaign could take New Hampshire, Iowa, Minnesota, and possibly Wisconsin. Mark Warner is a decent candidate - but he lacks accomplishment where as the public have given Giuliani the title of "America's mayor". I just don't think that people could warm up to Warner fast enough for him to beat the already tremendously popular Giuliani.
Seems to me that you are better informed about Giuliani and I don't know any polls for a Giuliani vs. Warner race, but I think socially liberal Giuliani would loose more in the South - especially against moderate-to-conservative Warner - then he'dd win in the Northeast.
The white blue collar workers in the North would also vote for Warner over Giuliani, in my opinion.