Canning will serve as the Padres' primary pitcher Wednesday in St. Louis, Kevin Acee of The San Diego Union-Tribune reports.
Canning has recorded a 10.12 ERA in the first inning this season and lefties are slashing .370/.475/.696 off him, so the Padres will avoid having the right-hander face lefties JJ Wetherholt and Alec Burleson in the first frame. Bradgley Rodriguez will take the ball first for the Padres on Wednesday as an opener.