In parliament, Trudeau yesterday pledged to prosecute those who broke Canada's anti-terrorism laws by joining the IS group, but also said his government would try to reintegrate them into society.
"We recognise the return of even one individual (who joined the IS group) may have serious national security implications," Trudeau said.
"We are going to monitor them. We are also there to help them to let go of that terrorist ideology," he added.
Only two returnees have been prosecuted under Canada's anti-terrorism act, so far.
Public Safety Minister Ralph Goodale last week explained the difficulties of gathering evidence in war zones for successful criminal prosecutions.
He rejected, however, the use of extra-judicial killings used by allies to solve the problem, telling public broadcaster CBC: "Canada does not engage in death squads.