You are comparing apples and oranges in a sense here, because the HV20 is a hi-def. camera while the GS500 is standard def.
The Hv 20 has manual controls but they may not be as useful as the GS500, for example the GS has a focus ring behind the lens, while the Hv has a thumbwheel........my best advice would be to go into a store and look at both models and see which has all the features you want.
Panasonic GS500 or Canon HV20
