The stamp is really not common and as no legal value. They clearly told my wife it's just a souvenir for you. The CoPR letter will be handed to you at your landing appointment and it will be directly activated. As
@profiler said, there is no need to go to the border and as he also said, it's recommended to avoid doing so.
Those that have to go to the border are from different programs, like skilled workers that applied from within Canada or also family class sponsorship but that applied using Outland route.
So don't stress with the stamp, most likely you won't get one as it has no legal value. And don't worry about the border, you will "land" in Canada at your landing appointment. That will be the equivalent as entering the country there, on site of the interview.