The London Police Service say they will hold a news conference at 12:30 p.m. ET.
Danah McKinnon-Bozek, who was pregnant, and her two daughters were among those rushed to hospital on July 25 after the driver of a red Monte Carlo reversed through the front entrance of a local Costco store.
Her six-year-old and newborn daughters — the latter was delivered by emergency C-section after the accident — later died. The third daughter, who is three years old, is still in hospital.
Two other people injured in the crash and the driver of the car, a woman said by police to be in her early to mid 60s, were treated and released from hospital.
Police have said the investigation is focusing on a number of possibilities including driver error, medical distress, mechanical error, or a vehicle malfunction.