A commented explained the reason for this
The pirates cannot be prosecuted under Canadian law because they did not attack Canadian citizens or interests and the crime was not committed on Canadian territory.
At least the French don't have this problem.
They captured pirates who were attempting to hijack a Liberian flagged tanker. The pirates (excuse me, accused pirates)are being turned over to Kenya for prosecution.
From the BBC
A French naval frigate has docked in the Kenyan port of Mombasa carrying 11 Somalis accused of piracy.
French commandos captured the men last week after an attempt to hijack a Liberian tanker.
The Somalis will be handed over to Kenyan authorities for prosecution under a special agreement with the EU.