Crown rust, caused by Puccinia coronata f. sp. avenae (Pca), is the most important disease and yield limiting factor of oat production in eastern Canada. In this study 101 oat genotypes composed of 51 cultivars and 50 breeding lines from eight oat breeding programs across Canada were evaluated for seedling reactions to six common Pca races, as well as reactions to a bulk inoculum of Pca in greenhouse trials and for adult plant resistance (APR) to natural populations of Pca in field trials in 2014 and 2015. Sixty-six genotypes showed resistant reactions to at least one of the six races; of these, 22 were resistant to all six races. These 22 genotypes also showed resistance to the bulk inoculum at the seeding stage and to the natural populations of Pca at the adult plant stage, suggesting that these current and future oat varieties have effective resistance against the common races and Pca populations in the region. Eleven genotypes, including 12ANS03, AAC Bullet, CFA1213, CFA1306, Idaho, OA1301-1w-3, OA1369-5, OA1370-2, OA1371-2, OA1383-2, and Oscar, were susceptible as seedlings but resistant as adult plants. APR is proven to be long lasting and provides broad-spectrum resistance to Pca populations. The 11 oat genotypes identified with APR in the present study are more desirable as sources of resistance for breeding programs developing durable crown rust resistant cultivars for eastern Canada.