Playing HU 2/4 PLO....

Have played with villain decent amount and hes 3 betting slightly more than usual today...

400 effective stacks...KK99 on button open for 12, get 3b to 36, I decide to 4bet to 108 and he 5bets for 326

At this point I'm aware that hes pretty much always gonna have AA but my questions are A) Am I supposed to just call it off knowing he has AA? and B) Should I be 4betting to begin with and what to do when 5s are always AA?

Thanks guys.