Maybe an older version of the boy, like his future self. He comes back in the dream to show the boy what he can achieve in the future and gives him some advice on how to get there.
Well, since it's this boy's story, the main character is the boy himself, of course.
A shy and nerdy boy could be the main character. He's always been into books and science. When he is turned into a girl, he has to use his intelligence to figure out what happened and how to get back to his original form, all while dealing with the social changes like fitting in with the girls at school or in his neighborhood.
It could be a regular boy named Tom. He's an ordinary kid with a normal life until one day he's struck by a strange ray that makes him giant. As he tries to deal with this new situation, he becomes the main character of this wild 'giant boy shrink story'.
Perhaps the main character is a boy named Sam. Sam is a bit of a troublemaker usually, but being home alone changes him. He realizes the importance of responsibility. He has to take care of his pet dog while his parents are away. And when some unexpected events happen, like a small fire in the kitchen because he tried to cook something fancy, he learns from his mistakes and becomes more mature in the process of dealing with these situations.
The main character, the boy, might be a bit of an outcast. He doesn't fit in well in his community, so he often retreats to the forest. There, he feels more at home among the trees and the animals. He could be a creative and imaginative boy, always dreaming up stories about the forest and its secrets.
The main character would obviously be the boy. He could be a curious and adventurous kid who is open to new experiences, which is why he might be able to handle being in a girls' camp.
Obviously, the main character is the Whitman boy.
Well, without reading the story, it's hard to say exactly. But generally, the 'Brooklyn Boy' would be the main character.
Since the title is 'it's a boy christmas story', the main character is a boy. He could be any boy really. He might be a shy boy who discovers his confidence during Christmas, or a naughty boy who learns to be good. There are so many possibilities without more details about the story.
I'm not sure as the 'dream girl story' is not fully defined. But it could be the girl herself if the story focuses on her life, dreams, and experiences.