Neil Bantleman, who worked at the prestigious Jakarta International School, was arrested during a police investigation into the alleged sexual assault of three kindergarten students.
His brother, Guy Bantleman, said from Toronto that the prosecutor in the case has not released the details of the charges but is expected to do so later this week.
He adds that his family had hoped for Bantleman's quick release when he was detained along with teaching assistant Ferdinand Tjiong in July.
Both men have denied the allegations since their arrest.
Indonesian law stipulates that police can't hold someone for more than 120 days without pressing charges, and Guy Bantleman says his brother has been in prison for 108 days.
Local media reported that the police investigation began with the arrest of six outsourced cleaners accused of allegedly raping a young boy in a school bathroom in March.
The Jakarta Post reported that the parents of two other students filed police reports claiming their sons were sexually assaulted by teachers.
The newspaper also reported that police claim to have proof the two teachers drugged kindergarten pupils before sexually assaulting them. Both Bantleman and Tjiong could face up to 15 years in prison if convicted.
Guy Bantleman says his brother is "distraught."
"He was really focusing on being released on day 120," he said.
Following the men's arrest, the three founding embassies of the Jakarta International School issued a joint statement that said Australian, British and American officials are "deeply concerned about the detention of several JIS teachers."
The Department of Foreign Affairs, Trade and Development says Canadian consular officials in Jakarta are providing assistance.
Neil Bantleman of Burlington, Ont., moved to Indonesia four years ago with his wife, who also teaches at Jakarta International School.
The couple previously worked at private schools in Calgary and at the Canadian International School in Singapore.