Is there a Henry's in your town? I live in Ontario and I think Henry's has a cleaning service. If not there is a canon service centre in Mississauga.
I have heard a few horror stories about cleanings at Henrys.... I would send it to Mississauga. This is something that you really want done right.
You are talking about a spot on the sensor which is NOT dust. If it is tree sap, you are talking about a wet cleaning so you can ignore everything you have been told about cleaning dust off your sensor... those techniques will just make it worse in your case.
Send it to Canon and tell them what you suspect the spot is...