Mario Wint, 29, was charged last week with second-degree murder in the death of his two-year-old son Mathias.
Wint was charged two days after York Regional Police were called to a residence on Longford Drive in Newmarket, where the boy was found not breathing. He was later pronounced dead in hospital.
Police won't say how Mathias died.
But friends say it's not possible Wint is to blame.
"Mario is a great father," Nayomie Little told CBC News. "He loved his kids. They were very well-behaved. They didn't have any sign of distress. They were well fed, well taken care of and this is just ridiculous."
Friends said Wint recently won sole custody of Mathias and another son. Prior to that, his visits with the boys were supervised by the Children's Aid Society in Barrie.
"He went through a long, lengthy fight — so to have this happen, it's almost unbelievable," said friend Sean Pitts.
More than 1,000 people have joined a group on Facebook to show their support.
Wint's lawyer, Steven Skurka, said he is waiting to find out what evidence the Crown has and that he plans to ask the court to grant Wint bail.
"My client is holding up well. He's in a solemn, serious mood. He understands the gravity of the charge he's facing," Skurka told reporters.
Wint is expected back in court next month.