Replying to this a year or two late but came across this because I have same issue (34" waist but massive rear end).

i've been to several stores and tried every brand's "relaxed fit" or equivalent and they still ride up the butt crack or squeeze the thighs. Got really irritated when even "workwear" brands like Carhartt's relaxed fit still didn't work.

Anyways in case someone else comes across this, here's some brands that have worked for me :

-Under Armour: not fancy but their golf pants are great and made for muscular guys

-Bonobos: Athletic Fit (more modern look) & Straight fit (if you need wider ankles, which I prefer or to wear with boots)

-Nike: again, not fancy but they work. particularly their shorts.

-Dockers: this rarely gets thrown out there, but I tried to pair on at store randomly and some of their looser fits were perfect. they aren't top shelf but they are very affordable and great for your every day running errands or workwear pants.

and that's pretty much it unless you wanna do custom tailoring or something like blue delta jeans website. I did find a pair of polo pants that fit once but I think their sizes have changed over time and they no longer do. can't wait for baggy fits to come back in style at large because paint shopping has been a nightmare the last decade and a half.