The Riders recently acquired Collaros in a trade with the Hamilton Tiger-Cats.
The 29-year-old University of Cincinnati product is a veteran of six CFL seasons. After spending his first two years with the Toronto Argonauts, Collaros signed with Hamilton in January, 2014 as a free agent.
Over the last four seasons with the Ti-Cats, Collaros has completed 930 of 1,396 passes (66.6%) for 11,342 yards and 66 touchdowns in starting 43 of 53 regular-season games. He also started two playoff games and the 2014 Grey Cup.
Collaros was named the Tiger-Cats’ nominee as Most Outstanding Player in 2014 and 2015.
He won his first career Grey Cup in 2012 as a backup quarterback with Toronto.