The current migrant health literature tends to focus on what determines immigrants' mental health rather than how pathways such as psychosocial resources mediate the relationship between years since migration and mental health. Based on 4,282 foreign-born Canadian immigrant samples, this study includes both psychological distress and positive mental health as mental health measures because immigrants do not necessarily respond to stress by exhibiting distress. The correlation between psychological distress and positive mental health shows that these two measures are interrelated but distinctive concepts. Using piecewise regression models, this study finds that midterm immigrants have the highest levels of psychological distress and interpersonal strain. Guided by the stress process model, this study indicates that interpersonal strain acts as a major pathway to immigrants' psychological distress but not positive mental health.