With El Al, you're interrogated before you board the plane. When you go to check in, there is a "pre check-in" where you show staff your passport and they check your name off against a paper list. That paper list would already indicate whether or not you're going to be interrogated and at what level.
My coworker flying with me was also red flagged, and he was explicitly told it was because of my country of birth and that he was flying with me.
He had much less of a rough time than me, though, where I was being interrogated over where I got the 100 shekels they found in my wallet (apparently exchanging a nominal amount of Aussie dollars for shekels at Sydney airport "just in case" astounded El Al security, and it was much more likely that there was something much more sinister going on).
The interrogation interests me. It sounds you don't feel it was useful? I had heard about this kind of interrogation over mundane stories, and understood it as a way of "testing" individuals' stories (especially under duress). But that would depend on it being repeated/prodded thoroughly, which it seems isn't the case.
If you're a regular guy, you're likely to react by becoming bored and tired. If you're doing sinister stuff, there is a chance that you might start to stress out from the interaction. I believe similar techniques are used when screening people for government security clearances using a polygraph. They seem to push people hard and accuse them of lying. I can only assume it's with the intent of causing legitimately guilty people to "crack".
I am not trying to justify the practice, just speculating about the purported rationale. Not a very fun experience as an innocent person.
The takeaway I got is that they just don't want people to visit Israel and made it as difficult as possible for me (which involved taking away my personal documentation, such as my invitation letter and copies of my citizenship, to give me a tough time when I got to Ben Gurion).
It was bizarre.
But then, I'm Jewish Israeli, so I don't have a lot of first-person experience with the full interrogation experience, just second-hand accounts from both sides of the table.
They tried to intimidate me with their faux "all seeing eye" - asking about whether or not I trained judo (in reference to the jiu-jitsu Gi I had in my luggage) but aside from that, the questions about the shekels in my wallet and also taking issue with the rubber waistband on my pants, they didn't really ask about anything else. The shekels thing and the issue they took with it was just absurd.
It was really just civilian employees on a power trip trying to mess with me... because they can.
Is this what Canadian border guards are supposed to be doing? I hate dealing with them, and therefore minimize my border crossings. I just want to pour money into the Canadian economy as a tourist from time to time, and actual Canadian cops (RCMP) are much less aggressive than their US counterparts, but the border crossing is almost always unnecessarily miserable.
If that's not the case, would you mind providing some details about your own experience, since you mentioned being pulled aside repeatedly?