Canola crops leave an average of 2-3 bushels per acre of seed in the field, or at least 20 times the seeding rate. Swathed or standing crop hit by heavy winds or hail can increase this number significantly. Reducing harvest losses is a good way to increase harvest yield, and it also limits the volunteer canola seedbank.
The first step in canola volunteer management is to do nothing. Leaving seeds undisturbed so they germinate in the fall or get eaten by birds and insects is a good way to reduce the volunteer seedbank. Canola seeds that remain on the soil surface when the snow flies will deteriorate over the winter.
If you want to do something, recent research from the University of Manitoba shows that a light pass with harrow after canola harvest stimulates the germination of volunteers and reduces seed bank additions by as much as 50%.
When full tillage is necessary, hold off for a few weeks if possible to allow predation and seed germination before seeds are buried. Keep in mind that burying the seed can induce seed dormancy, keeping that canola seed viable longer, possibly for years.
Canola Encyclopedia section on volunteer canola management
Rotations for weed management