Since PCGS is recognizing the 67 doubled die, I went to their website but could not find any info nor listing for a tripled die or a doubled die for that matter.
I know even if it was a doubled die or a tripled die variety it probably wouldn't even have any value to speak of, but those serifs are definitely doubled.
IMO it is MD, for the following observations A/ The "doubled" image should be raised not flattened almost to the coins surface. B/ The movement of the die during striking has narrowed the width of the numbers whereas with a doubled die they would look wider than normal
I understand what you're saying, but I wish that I come across some close up pictures of the doubled die that PCGS recognizes to compare the two.
These images seem to be very like yours https://www.pcgs.com/news/now-recognizing-canada-1967-doubled-die-obverse-cent
It looks like DDO with MD. The MD messes up the eye a bit, but clear doubling on the letters. I have a bunch of these coins...perhaps almost a roll accumulated over the years. I will need to dig that out now.