Which are correct:
1) John is the man who will meet you at the airport.
2) John will be the man who will meet you at the airport.
3) John will be the man who meets you at the airport.
Is there any difference in the meanings?
Grammatically, they are all correct, but the red sentence is a bit awkward, with its seemingly unnecessary duplication of the future tense. I like (1) and (3) much better, especially if you have in mind all three sentences meaning the same thing.
In our contextual vacuum, it is easy to fancy that you have in mind a single meeting event. But habitual readings are possible. Sentence (2) could mean that John will be designated the person who will regularly meet you at the airport.