While Revan's gender is specified by the player, the canonical Revan is confirmed by Leland Chee to be male [1]. Also, The New Essential Chronology and the Chronicles of the Old Republic, published prior to the release of The Sith Lords, both refer to Revan as male.
In KOTOR II, if the player chooses not to define Revan's gender during an important conversation with Atton Rand, the game sets Revan to a light-side male by default. However, it is notable that Atton, at first, apparently assumes Revan to be female. This may well have been a genuine mistake, or just an attempt to hide his past. The actual physical appearance of the character has not been defined in continuity.