Believe it or not I used to be painfully shy.
If you feel the same, don't let it hold you back from trying. It sounds as if you are a nice guy, and this could work to your advantage when you go canvassing.
When I canvass (as I am still building my business up) I say something along the lines of "Hello, my name is John, and I am offering a window cleaning service locally. Is this something you may be interested in?"
I put this across with a smile, and relaxed manner, and even when the reply is negative, it is usually accompanied with a smile, and sometimes even apologetically from the householder. So the rejections can even be a source of encouragement to carry on!
As Ian Lancaster said, it's a free market so you can go wherever you want. If you meet another window cleaner, and he tries to put you off, tell him you aren't looking to take his customers but are looking for people who need a window cleaner but who haven't got one.
Best wishes,
John