The 6-foot-2 inch Harrell, a native of Ennis, Texas, was told during individual workouts for teams last spring that he lacked the necessary arm strength to be a quarterback in the NFL.
He was not selected in the 2009 NFL Draft in June, so he thought his stock would be higher in the CFL.
The Roughriders did not say when he would suit up for his first professional contest.
The NCAA's all-time leader in touchdown passes (134), also threw an NCAA-record 512 completions in 2007 and was the only collegiate quarterback ever to pass for at least 5,000 yards in one season twice -- 5,705 in 2007 and 5,111 yards in 2008.
Notable deaths of 2014 [PHOTOS]