The Traffic Safety Act 222 - Backing up
No person shall cause a vehicle to move backward on or onto a highway unless the movement can be made safely.
How the rule is applied
Collisions while backing up are among the most frequent type of collision. Never back a vehicle until you have checked behind it from outside. The law says that the onus rests on the vehicle backing to not do so unless the movement can be made safely. The driver backing up would be considered responsible and deemed 100% at fault.