Opioid agonist therapy is a key element in the response to opioid-related harms in Canada. In May 2018, Health Canada rescinded the requirement for obtaining a federal exemption for methadone prescribing. This comparative analysis examined OAT policies and policy changes in response to this federal policy change. Policies and changes were regionalized: despite having lower rates of opioid-related harms, Eastern provinces had looser regulatory regimes compared to Western provinces, which became even looser after the federal policy change. Diverse knowledge and policy networks need to be fostered to bridge this East/West divide in substance use care policy.