I bought a magnolia branch at a garden show, vendor said stick it in water and the buds will open. They didn't, but a green shoot has appeared at the base! there are white nodules at the bottom but no roots yet. Should I cut the top off? leave it in the water until I see roots?

I'm in Toronto so I guess this is a hardy magnolia. Assuming it is established, do I plant it out in the garden this year? how long before flowers appear? thanks!