Beneficial nematodes will take care of most ants - definitely will stop fire ants. Nematodes are microscopic living organisms that live in the soil and eat the fire ant eggs - also FLEA eggs (YAY), grub eggs, and the eggs of anything that lives in the ground. Here is a website that tells you about them.
Beneficial Nematodes - Organic Insect Control
They are completely harmless to plants/animals/humans. You can usually buy them at an organic plant nursery. I'm not sure they have them in Canada - but you might check. They definitely should have them in Florida. They must be kept cold (in the fridge) until they are applied and you have to follow the application method exactly.
I've used them for about 10 years now and never have any fire ants in my yard or garden. No fleas either! YAY!