I've gone to this place to get my back done a bunch of times (not that I have lot hair on my back) but when I've gone on vacation I just like it gone if I'm at a pool or on a beach.
I'm pretty sure they do male buttocks and they're very discrete and private.
https://www.aromawcs.ca/
I've been thinking about getting laser hair removal on back and buttocks, but I'm not totally sure if the place I'm looking into does male buttocks. I don't the time right now anyway, but something I'm considering for the future when I have more free time.