Hi Paul.
Your post that you want to leave your job to do window cleaning but you do not have the time to spend canvassing.
I have never used a canvassing company but can see their worth when your business gets to a point where you need say a final 100 customers to compleete your round.
Reading your post it seems that you want or need to hit the ground running with an income.
The only way to do this is to buy a round and work with the person selling, if you really do not have the time.
Finally, and without wishing to seem rude, what makes you think you can/want to clean windows? Most successfull window cleaners spend a lot of time refining their work, managing their time and growing the business.
It is not an easy option, whereas your post makrs me think, you think it is.
If you do it, good luck
Tony