Defending Domestic Produce Production Act of 2021 This bill establishes a process by which a core seasonal industry may petition for countervailing and antidumping duties. A core seasonal industry means the producers (1) of a domestic like product that is a raw agricultural product, (2) whose collective output constitutes a majority of the total production in any state or group of states that accounts for a major portion of the total production during a discrete season or cyclical period of time, and (3) that make substantially all of their sales during that season or time period. The bill also provides that this process shall apply with respect to goods from Canada and Mexico.