The owner of the Australian Shepherd dogs, Mike Morrison, called the OSPCA after the family pets suddenly became sick with the same symptoms on the property, near Vandorf Sideroad and Kennedy Road.
Morrison says he doesn't know how they came to ingest the toxin and that he didn't have any of the chemical on his property when the dogs became ill over the weekend of Jan 9-12.
The OSPCA on Thursday said it's seeking possible answers from the community as it works with York Regional Police.
The owners reported that one of the dogs has tested positive for ethylene glycol (antifreeze). Testing is still underway to confirm what is suspected to be the same kind of poisoning in the other two dogs.
Brad Dewar of the OSPCA said all three dogs died within several days of ingesting what was suspected to be antifreeze.
Ethylene glycol can be extremely toxic and often attracts animals because of its sweet taste and smell.
"In cases where antifreeze is used to poison animals, it is an offence and a person could face charges," said OSPCA regional inspector Alison Green.