Hello GB,
Of the three, email canvassing is the one thats easiest to do - but possibly least effective as it will either not reach the right person or will be treated as spam. A few years back I did a fax campaign which was 100% unsucessfull

I would use telephone canvassing as an opportunity to find out who is responsible for arranging window cleaning etc. then ask if they're available or ask to make an appointment
or, if you have their name, when passing you could call in and try and see if they're available or again make an appt. The advantage of being on their premises is that you'll see closer up the condition of their windows etc
The hardest part of business to business sales is actually speaking to the right person, don't try and sell to everyone in the company.
Good luck, Dave
p.s. if SAJ agrees can I have a gander at his documents pls