All of the 3400-4000 series saws I have that were made in Ontario, came equipped with a chain brake. The early ('79) one from the States I have, came equipped with a chain brake as well. But, it was the original solid arm/flag style. I can't say what the deal was, as the other big saw factories in Canada were not necessarily equipping saws with mandatory brakes then. I am not sure if you could have bought a 3400-4000 during that period that was Canadian made and had the option of no chain brake. I am too young to have been shopping then but am curious nonetheless. I am not sure if there were different Canadian regulations for homeowner versus pro-class saws. I have micros, s25da's, etc. from the same era that do not have brakes.
Those 3400-4000 series brakes do add mass though, as the covers are all Mg. They are easy to engage/throw. Not the best design overall, but have at least proven themselves for me in a couple of situations.