The border crossing is from Poland but most likely they did not directly fly from Canada to Poland.Most likely they went from Canada to some western European country (or, better, to a neutral country such as Finland or Sweden) where they acquired the Volvo but this part of the scenario is a bit unrealistic because driving with a western passport all the way into Poland with a western-registered car towards the Soviet border would be both risky and unnecessary.
The border crossing had signs in Polish.Thus, in my humble opinion, they crossed into the Soviet Union from Poland.
My guess: flight to Helsinki with the road trip to Leningrad leading them to take on of the two major border crossings on that route: Although they drove a Volvo, there is no evidence that they took the ferry from Stockholm.
probably Poland, it’d be easiest for a crossing there.
I found the Bono song to be quite ironic, as Im sure he did.