I personally think canvasing work is better because you dont have any outlay, you can price the work, you can pick the type of work and you and the customer know what to expect from the start.
Door knocking is definatly better than leaflets as you get a decision there and then, the potential customer dosnt have time to put the leaflet aside and forget about it. Taking a note of properties where no one is in and calling another time is also a good idea as you can get to everyone who you would not normaly see. leaflets are good if you cant find anyone in or if you get a job you can leave one, the customer then has your full range of services for the future.
Others have bought work though and have done well out of it.