the person who opened the door
The driver/passenger opening the door is at fault. Look it up under the traffic laws in your state.
driver of parked vehicle
The person who opens the door.
The insurance company of the car whose door was opened will pay for it.
I cannot speak specifically to Canda, but in the US it would be the opening door vehicle that is at fault, most of the time. You cannot open or enter any traffic until safe to do so.
The person that opens the door is at fault
Virtually ANY time a vehicle door opens into moving traffic it will be the responsibility/fault of the party who was in control of the door. The questioner states that they were CLOSING the door??? That may be their story, but it will probably be difficult proving it.
This type of claim can go either way. It could be said that the passenger should have looked before opening the door. It could also be said that the driver of the other vehicle did not have the right of way going around on the passenger's side. It is up to the insurance companies to decide. If you are getting resistance from the other driver to claim responsibility, you should make a claim with your insurance carrier and contact a car accident attorney immediately as the insurance carrier may not want to pay for the damages. Fisher & Associates in Colorado is proficient in these kinds of cases.
I know of a case where a person opened a door on a narrow road and it was struck by another vehicle driving down the road. The person opening the door was at fault. Your situation sounds a bit different but the person opening the door may be at fault.
Dextral opens to the right, sinistral opens to the left.
The one backing out, because you should realize someone is opening a door.
If your the uninsured car was parked, and the door was already open when it was struck, then it would be the other drivers fault. If you are parked then you are classified as a permanent object, and you are treated just like all other permanent objects such as trees and signs. The other driver must have control of his vehicle at all times, and by hitting you while you were stationary and not moving, this was not the case, so he is at fault. Now if he was driving and you opened the door right as he was passing you, then the answer would not be as clear cut.