umm, no, the way you think is not the way it is...They don't act as a spoiler.
Apart from cutting bystander's knees in half, Canards mounted on the front bumper lead to an increase in downforce and decrease in drag by causing the air flowing by the sides of the car to tumble, i.e. roll by the side, similar to a venturi effect. What this achieves is that you have an area of low pressure flowing by the side of the car which cuts down drag as well as increasing downforce by reducing the escaping of air from under the car via the sides of the car (i.e. under the sills)...
The air "pushing down" on the canards has negligible effect as the canards themselves are too small in area to generate any meaningful effect