Polls have been done that pitt John McCain one at a time against John Kerry and John Edwards. The results show that if the election were to be held today, McCain would beat Edwards 46% - 43% and would slaughter Kerry at 51% - 41%.

In two separate head-to-head contests, McCain holds a 10 per cent lead over Massachusetts senator and 2004 Democratic presidential nominee John Kerry, and a three per cent advantage over former North Carolina senator and vice-presidential choice John Edwards.
Source: Angus Reid

This adds to the evidence we’ve already seen (like When McCain told Kerry to give it up) that the next election will exclude the John/John ticket of 2004. Giuliani is traling McCain by a moderate margin but both of them are set to be likely candidates for the GOP. The Democrats have Hillary in a ridiculously strong lead so early on, but her competition has plenty of time to create an attack plan against her. It’s just as likely that we’ll see some newcomers to the primaries like Russ Feingold or even a returner like Wesley Clark (I hear he learned how to debate and give speeches since last election).