"May you please stop" is a polite request, implying that the speaker is asking for the listener to stop doing something. It's often used in formal situations.
"Will stop" is a statement of future intention. It suggests that the speaker will stop doing something at some point in the future.
Here are some examples:
* "May you please stop making so much noise?" (Request)
* "The train will stop at the next station." (Statement of future action)
In short, "May you please stop" is a request, while "Will stop" is a statement.