You need to read your Breeders contract carefully to see where you stand.
In CA, we have a Doggy Lemon Law but, not sure what recourse you have in Cananda.
Most of the time (in CA), you can still keep your dog and the Breeder becomes responsible for the $ care of your dog.
Other times, you must return the dog in exchange for a replacement puppy or a refund.
My concern with returning a dog who has medical issues is what will the Breeder do with this dog? If the Breeder is not reputable or ethical..."your" dog could be euthanized!