I'm with several others in this thread wondering where the "both FemShep and MaleShep" options are. That said, I'm a guy, and my canon Shepard is a male, so I guess that the first option applies. That said, I've played through the entire trilogy with a total of 8 Shepards - half male, half female - and I'm currently playing and planning several more playthroughs for each gender.
My canon Shepard (and canon Warden in Dragon Age) being male just comes down to the fact that I know I'll play the games several times and get to play both genders, and then I guess I just like to start with my own gender. It's also that my first/canon playthroughs are often a particular kind of character which I personally like to play as male. But I'm totally open to playing a female and often do when I have the chance.