Carrie Underwood rocked a fabulously casual double denim look on Monday as she rehearsed with Jason Aldean for the upcoming Country Music Association awards.MORE: Carrie Underwood overcome with emotion after major surprise during Nashville performanceThe singer and Jason will perform their duet If I Didn't Have You live together for the first time, and Carrie shared that it is "really exciting".WATCH: Carrie Underwood and Jimmie Allen discuss 2021 CMAs"We faked it about a hundred times for the