"...Including for US commissioned peace officers?..."

Pretty much. I know of two CA peace officers who left their issued handguns, along with a hefty fine, in Canada when they got caught with them at the border. I also know of one officer, who was involved in a "cop ride" murdercycle ride from Cal up thru a lot of Canada and back. He managed to get a permit to bring two handguns with him. I don't recall the details, it was too long ago, but I think he got himself entered in some pistol match in Canada, which allowed him to carry the weapons, but not on his person, and not loaded.

It is pretty easy to bring certain rifles/shotguns into Canada, I did that a couple of years ago...