What will you do/are you going to do/are you doing?

Hi!

1- What will you do on your vacation in May?
2- What are you going to do on your vacation in May?
3- What are you doing on your vacation in May?

I came across these three sentences this afternoon. It's interesting that the book said there's little or no difference among them. If you ask any native speakers, they might want to thrash your head. In my humble opinion, there is little, very little difference there. We had that topic at a time last year. This is how I interpretate.

The first one is a simple inquery to know what will you do in a future time? It's like "Where will you go when you get there?" The questioner does not cast any prediction at all. The second is of intent as in "What do you plan to do?" The last one may imply that the questioner has presupposed that the person he's talking to has already planned something in advace.

I think they're almost the same. With the word "almost", it means there is nuance. I look forward to hearing from you.