Is Haku a man or a woman?
I do not think that Haku was considered as a woman is considered a spoiler. 

After all, they discover that only 1 episode after Team 7 met him. I can guarantee for sure that Haku is a man. Despite what other sources probably say, there are plenty of men in real life who look like women (Justin Bieber is good example). What I cannot tell you is what was the perspective of Zabuza for him (if he was just a Friend or something "Else").

I say this only because the one who told Naruto that significant detail was Haku himself, so there isn't a lot of room for mistakes.