Straight men don't get erections easily with women, but they do with men:

An attractive woman's experience of giving massages to straight men:

Getting an erection during massage is not normal (as in it doesn’t happen every time) but it does happen. I have given massage for 20 years full time (probably around 20,000 massages) and I have only had one male get a full on erection. I know there are probably more who have had feeling stimulated or had the massage feel sensual.

Julie Onofrio, LMP

A man's experience of giving massages to straight men:

I have had heterosexually identified men become aroused during a session. I have even had heterosexually identified men become aroused during CranioSacral Therapy Sessions which are performed fully clothed. As the body relaxes deeper into parasympathetic, the odds of arousal increase. While working on the sacral, lumbar, and pelvic areas of the craniosacral system, I am working specifically in the area of the lumbar sacral plexuses talked about above. I have also spoken with other male massage therapists from around the country who have had heterosexual men become aroused during a session.

Cranio Brian