The Detroit Tigers are trying to resign Anibal Sanchez, and won't want to pay arbitration for Porcello.Castellanos is blocked by Miggy. Garza would strengthen their rotation for a year and Marmol could fill their closer role left open by Jose Valverde.
Cubs are trying to part ways with Marmol anyways and get a young midrotation pitcher in return. Castellanos could be the third baseman of the future without giving up too much. Cubs would probably have to eat some or all of Marmol's contract but there could be a match here