This chapter examines climate policy efforts across four Canadian subnational jurisdictions that joined the Under2 Coalition at different timepoints: founding members British Columbia and Ontario, early joiner Québec, and later joiner Northwest Territories. The analysis compares the adoption of climate policy, policy instruments, and greenhouse gas emissions reduction targets to assess whether founding members demonstrate greater climate ambition than subsequent joiners. British Columbia exhibited sustained climate leadership before and after co-founding the Under2 Coalition, while Ontario’s trajectory was marked by political instability and policy reversals. Québec, despite being only an early joiner and not an Under2 Coalition founder, demonstrated robust climate action intertwined with resource nationalism and paradiplomacy. Northwest Territories, as a later joiner, showed limited policy activity but place-specific innovation in addressing energy needs of remote community. The findings reveal that early Under2 Coalition engagement (whether as founding member or early joiner) facilitates maintenance and enhancement of climate leadership, though context-specific factors—including federal-provincial fragmentation, political transitions, and resource dependencies—significantly shape subnational climate action trajectories and climate policy durability.