Canards don't generate that much down force. Think of them more as vortex generators that
help the air flow around the front wheel arches and down the side of the car. An air dam, flat floor and diffuser are the way to go with your car.
Down force front and back needs to be balanced and it's much easier to generate front end down force. You'll get more benefits from a flat floor and diffuser than 'just' more down force. Think also less drag. You can't be that much older than me and I plan to spend a bit of time this summer on my back with some big bits of cardboard.
If you haven't have a look through that thread I posted a link to, it's impressive stuff!