2k a month of extra work! Easy if you break it up.
Go and find 1000 sold boards over a 10/15 mile radius, at least 20% will want a window cleaner for there new home, charge £10 a pop and Bobs your uncle.
Find all the new build estates that have just gone up or in the process and hit them at every possible chance, new build customers are easy to get although competition is more fierce as many have the same idea so best to get in quick. With enough new build areas within distance you would find 200 £10 jobs easy.
Go on wforsale.com and buy the 2k of work as you must be doing well if your going to go the franchise route.
Or do a mixture of the 3
Id avoid paying a canvasser unless your going to be doing all the first few cleans yourself as otherwise when the canvasser phones to query all the dropouts you wont have the reason that the franchisee didnt do a good job on the 1st cleans which i found happend all the time canvassing for franchise outfits.
You can do it, you don't need anybody else other than yourself and a bit of positivity to hit your target.
Go and smash it :-)