Rehtaeh Parsons died in April, in a case that gained nationwide and international media attention over the scourge of Internet bullying.
Parsons was believed to have been bullied mercilessly after being sexually abused by four boys at a drunken party in 2011.
Photographs of the abuse were reportedly circulated on the Internet and among her classmates.
The Police had decided not to press charges in the sexual assault allegations but came under renewed pressure to reopen the case after Parsons' death in April.
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"They are in police custody and are currently being questioned by investigators," the statement said.
The arrests have come one day after the adoption of a new anti-cyber-bullying law in Nova Scotia, Canada.
Prime Minister Stephen Harper welcomed the apparent progress in the case and vowed to review national laws on cyber-bullying.
"I just wanted to say how pleased we are that progress is being made. I hope this will provide some measure of comfort to the family members," he said.