If you only have had your camera for a year, Canon will do it for free. My 1Ds Mark III just went in 2 weeks ago, still for free, for a sensor cleaning. Doing it yourself with a puffer usually doesn't work very well.I am sending mine in to have the light leak issue fixed on my 5D3 - it is only four months old - are you saying I could ask for a free sensor cleaning too?
The first time I took my 5D2 in for a cleaning, it was still under warranty and they did it for free. Just note that they might only do it for free the first time.