1) Why would you assume that one man can't overpower another, that it would have to take at least three? People have different body structures and have varying levels of physical strength, so one man can definitely be strong enough to overpower another man.
2) Why isn't it possible for a girl to rape a guy? Again, there are strong people and weak people, so a girl can definitely be stronger than a man.
3) What if the man is disabled, thereby limiting is physical ability to defend himself?
4) What if the man is emotionally weak, example, traumatized or afraid or sad, so much so that he can't defend against rape?
5) What if the man is gang-raped by several men and/or women?
6) What if the man is chained or restrained so he can't protect himself?
7) What if the man was drugged and becomes unconscious?
To answer your question, men can definitely get raped, be it by another man or men, or woman or women. On a side note, they can also experience sexual abuse and/or sexual harassment, and this may not necessarily be rape.