I've been canvassing myself over the Xmas period and have also used the services of Paul at Doorknockers. The results have been extremely pleasing (Paul's slightly better than mine) and although some people have asked for the 1st clean to be in January, they've still committed to using me - most just want them doing straight away.
You can also give people the option 'Would you like them doing now, or leaving til the New Year' it's a better close than a 'Yes/No' question.
Either way I reckon it's well worthwhile going canvassing and leafletting in Xmas, there's more people at home, people are in a slightly better mood than normal, and if you sense that money's tight for them you can come across as caring, compassionate window cleaner by suggesting that they leave it til January.