To the OP, welcome!

As for your question, my response would be pay the fine and get it over with.

If you were traveling 50km/h over the limit (almost 2x the speed) and got the ticket from an officer, any protestation should have been at that point if you felt that there is no way you could have been traveling that fast. In the end, it sounds like you got a big fine, but not the maximum penalty possible so in some way, the officer was doing you a possible favor.

As for why I would pay, there is a possibility you could get away with it if it does not go through your rental agency, there is no communication between ICBC and US authorities and you have no intention of entering into Canada. Those are 'ifs' that I am not sure are worth the <$200 fine.