I was reversing in parking lot when a car went behind me and I backed into him. Who is at fault and who pays for the repairs

Please give more information.

Why were you backing up? Were you backing out of a parking space?

Were the police called?

Do you both have auto insurance?

Unless police were called to render judgement, there is little to do as it will be a he said/she said. Generally you will be alleged at fault for not having a clear line of sight and still backed up. "I backed into him" infers your fault. Most providences in Canada have no fault auto insurance.

Generally, a car backing out of a parking space has to yield right of way to vehicles in the lanes. So the car backing up is probably at fault.

But the question only matters to you if you don't want to go through insurance. Usually you just file a claim with your insurance carrier and they will hash it out with the other driver's carrier.

If you want to avoid filing an insurance claim, you try to negotiate with the other driver. But if it goes to court, the driver backing out of the space will probably lose.

In Ontario, involving a vehicular accident in a parking lot, which is private property, it is considered a no fault. In other words it is the responsibility of each party to get each other's insurance info and just basically 'duke it out'. The provincial police cannot favour on private property.