The crown prosecutor, Marie-Claude Bourassa, said the charges are connected to an armed robbery that took place on Jan. 2.
The 12-year-old boy faces charges of armed robbery, conspiracy to commit robbery, possession of a prohibited firearm, unauthorized possession of a firearm in a vehicle, and taking a vehicle without consent.
Bourassa said evidence suggests the same weapon was used in the robbery and the manslaughter.
Another boy in his mid-teens, alleged to be involved in the robbery, is expected to appear in court for a bail hearing on Feb.11.
On Jan. 22, the 12-year-old boy was charged in a youth court with manslaughter and possession of a prohibited firearm after his brother died from a gunshot wound. He entered a plea of not guilty.