Young canola plants can be taken out by various threats, including insects, weather damage, diseases and so much more. This article discusses the long list of reasons for missing plants.
But the plants might not be missing at all…they might just be “slow”. Dig around. The seeds might have germinated and the stems might be taking their sweet time in breaking the soil surface.
Why so slow? Could be soil conditions. Could be seeding too deep. Could be lack of vigour. But look closely. One of the various factors listed in the linked article could also be at play, such as seedling diseases, deadly rates of seed-placed fertilizer or cutworms.