Assuming Jeb also loses in Florida - the field would have opened up significantly had Bush not been there. Post-impeachment the party establishment really wanted to exclude the Congressional wing as much as possible, and Republican governors especially coalesced readily around Bush's huge establishment standing. There's just not going to be anyone to clear the field like Bush did.
John Ashcroft was interested in running and looked like a potentially strong candidate, but he was up for re-election in 2000 and Bush looked unbeatable, so he wisely passed. (He lost anyway to the deceased Mel Carnahan, though narrowly)
As noted above, John Engler (Who was given serious consideration as Dole's running mate in 1996) and Frank Keating might also have ran. But someone like John Ashcroft would be pretty damn strong in Iowa with evangelical caucus-goers.
I don't see McCain winning the nomination at all - IOTL he was really powering his bid on a lot of independent and even Democratic support from the open primary in New Hampshire, (Also Michigan, IIRC, but I may be misremembering that.) and actual Republican voters stayed pretty keenly with Bush. The party wasn't really divided. Also, John McCain was at peak John McCain and wasn't too circumspect about what he said. I think he'd be as just as longshot ITTL as he was IOTL.
I think the most likely outcome is an Ashcroft-Gore contest. I think the term for that is 'interestingly boring'.