There's a slight difference for me in these two:
- You shall win
- You will win
Shall, to me, here is an instruction to win to someone who is capable of winning this but is considering not winning (I.e. losing on purpose), or as a strong statement to put maximum effort in and ensure success. Will is a statement of confidence from the instructor to someone who isn't sure whether winning is guaranteed.
As a question:
To me means as you've put it- when asking another person, using shall would mean "I don't have to win this, but I know I can. What say you I embarrass my opponent by defeating him easily?". Using will means "I'm not sure if I'm going to win this, what are your thoughts?"
Other examples (not in the question form):
When my good hearted friend accidentally forgot to pay for something from the shop, and walked out with it:
"I think you will do the right thing and return it"
When my "bit of a bad boy" friend "accidentally on purpose" stole something from the shop:
"You shall do the right thing and return that item"
Third party examples:
- "the commentator clearly thinks the Jets will win" (opinion of success)
- "the coach told the team they shall win today if they hope to win the series" (instruction to succeed)
But really the second form might be better reworded to omit shall as it feels slightly out of place, and "need to win" or "are going to win" might better express the sentiment of whether it's an opinion or a requirement
See https://en.oxforddictionaries.com/usage/shall-or-will for more examples
Don't blindly and universally use shall; to this particular native English speaker it feels more formal/less common/more archaic than will; will is softer and less likely to be interpreted as imposing your desire on others, and this may be more appropriate in most situations