Shepard is male on the box, in the trailers ect. The character is written so that it can be both, but if you wanted to define something as canon, Shepard would be a male soldier class with a buzzcut. However, the whole point of mass effect is to create a unique experience for every playthrough, and choosing your Shepard's gender and attitude is part of that.
I'll admit, the VA for shepard is very clean cut and bland. I think bioware wanted to make the character voices generic, so that it would be more relatable, but they overshot it a bit when casting the male Shepard. The reason he's male in the "canon" is probably just because most gamers are, and so a placeholder character might as well be as generic as possible in respect to its general audience.
As for the "romance with Jacob" thing, there's a few things wrong with that.
1. Shepard doesn't need to show "humanity" because his/her personality is supposed to be defined by you. You choose what makes him/her tick. I haven't played as a girl, because I'm not female, and I want my Shepard to be as close to me as possible, but I would assume that introducing outside psychology to Shepard would detach me from the character more, unless it just so happens to be concurrent with my personality.
2. Traditionally, guys are less emotional than girls, or rather, they tend to hide their emotions more. Yes it's a stereotype, but the purpose of Shepard is, again, to be projected onto, and putting male gamers into a situation where Shepard is a gushing ball of emotions would be unrelatable to many people, especially those who want shepard to be a cold hearted killer or a suave playboy.
3. Might I remind you that Shepard is supposed to be a hardass marine in the first place?
Though all of this is irrelevant anyways. If you like the female Shepard better, play as her. If you're complaining that the default Shepard is male, you're just kind of making a big deal out of something that really shouldn't bother you anyways.