With canvassing its really a case of "winners never quit, quitters never win" write that somewhere where you can see it every day.
Of coarse most of them will say they already have a window cleaner. Its like all pretty girls already have a boyfriend. You are not going to stumble on a street with nobody already with a foothold.
Buy a streetmap of your area, and canvass every house on every street systematically. Don't go bouncing around here and there.
Its part of the reason I prefer leaflets, you can leaflet the whole map fairly quickly and you will get some bites. Then you can start to canvass around where you get the bites to build little clusters.
For volume I prefer leaflets, and you can go back over the ground and re-leaflet every three months. This is sound because often the third time round is more productive than the first. People start to recognise your leaflet.
For about the past ten years we have recieved the same carpet cleaning leaflet through the door about twice a year. I have never used them but I have passed the leaflet on to several other people.
If you are in it for the long game you can approach it this way.