Police say an autopsy will be performed today to determine the cause of death.
Jeffrey Boro, Havis's lawyer, says he believes the way Havis was arrested and held in custody contributed to his death.
"In the process when you arrest him as if he was a 25-year-old, he gets hurt. But everybody did what they were trained to do and in these circumstances all the training, as far as I'm concerned, brought about the death of my client," said Boro.
Havis was charged with 15 offences in connection with the standoff that began on July 30 and lasted overnight when he barricaded himself in his house near the corner of Guelph Road and Blossom Avenue.
Montreal police Const. Daniel Lacoursière said Havis did not have any life-threatening injuries when arrested, but was taken to hospital for evaluation.
Havis was hit by rubber-coated projectiles during his arrest, according to police.
His doctors delayed the court arraignment, saying Havis had both physical and emotional health issues, according to Crown prosecutor Matthew Ferguson.
Police found 180 firearms and other weapons in Havis's home after the arrest.
Officers were initially called to Havis's home about a dispute allegedly involving a firearm, between the homeowner and workers on his property.