Keep an eye on the brood nest. If they are fillling it with honey, and the queen has no place to lay, they will begin preparations to leave. Just assuming they won't swarm the first year is probably a mistake. In areas of strong flows, it can happen pretty fast, and once started, it's hard to stop. That's why just adding a super doesn't solve the problem. Also, with the intense flow generated by canola, they can run out of room pretty fast. Be proactive, not reactive, by makeing sure they are expanding the brood nest, not shrinking it, and they have room for nectar curing as they need it.
Look for some of Finskis posts. He builds up towering colonys and gives them lots of room to work rape seed in a very short time.