Police responded to the call just after 5 p.m. Wednesday in a residential area in Milton.
Halton Regional Police say the toddler's parents were at work, and the car had been driven by an extended-family member.
It’s not known whether heat was a factor in the boy’s death. Outside temperatures on Wednesday afternoon exceeded 30 C with high humidity. No criminal charges have been laid.
The red car, which had been parked just outside the garage of a home, was towed away late Wednesday by police.
The official cause of death will be determined after a coroner's examination on Thursday.
Halton police say the homicide squad is mandated to investigate the death of any child under the age of five.
Tow truck has removed the vehicle from Jempson Common in Milton where the 2 year old boy was found inside. pic.twitter.com/GsbkAhTWgq— DR (@Media371) June 27, 2013