Cohabitation has become increasingly accepted and normalized as part of the family system in Canada and has become the most common way to form a first union. The changing role of cohabitation in the family system is often understood as being driven by the ideational changes associated with the second demographic transition, but increasing international evidence indicates that this explanation is incomplete. Using nationally representative retrospective data from Canadians born between 1940 and 1979 from the 2011 General Social Survey, this study examines transitions out of first premarital cohabitation and fertility within these unions as two measures of the changing role of cohabitation. Across birth cohorts, Canadians are increasingly likely to use cohabitation as an alternative to marriage and less likely to use cohabitation as a short-lived prelude to marriage. These overall trends support the second demographic transition perspective. However, this study also finds that Canadians without a bachelor’s degree are far more likely to experience a birth within cohabitation and that their likelihood of transitioning to marriage has declined steeply across birth cohorts. This educational gradient in childbearing in cohabitation and the increasing educational differences in union transitions over time provide support for the diverging destinies thesis in Canada.