Whether he is within his geographical jurisdiction or not the Canadian courts have held that because he is driving the marked patrol vehicle, is a sworn police officer on duty, he has a legal responsibility to deal with the matter. Its like a Military Police officer in a marked car off base. He/she can still take action if they witness something.
As to the accuracy of the ticket, I'd be hard pressed not to challenge it IF it was me who received it. Most Canadian cops won't even issue a ticket for 5 km (2 mi) over the limit because that is within the generally accepted "margin for error" of a persons speedometer or the officers radar or lidar instrument.
IF, as you say, he didn't have radar then his estimate is purely subjective and cannot be substantiated by an instrument reading. Did you ask to see the radar/lidar and did he say that he didn't have an instrument or are you just guessing? Either way, challenge if it you want but be careful how you argue the point since you have already admitted here that you were speeding in order to pass him. Speeding is speeding and if you are going to make an argument then you want to be on firm moral ground.
It is not necessary to clock your speed on radar, and it is still speeding if you exceed the limit to pass another car. The ticket is legitimate.
YES they can. Railroad Police are in face sworn police officers and can cite you. If they know what speed they were going and you were going faster than they were and they were at or over the limit, then you were speeding and no absolute number is needed. Also, a recent supreme court ruling said that a trained officer who has undergone the proper schooling for speed detection can write a citation without using a speed measuring device, based on their training and experience. Also, is it possible you did not know you were on CN property? You don't have to be on the tracks themselves, the railroad usually owns a good deal of property aside from the tracks themselves.
If he was doing the speed limit and you opassed him - you were speeding.