First time poster here. Please don't beat me up too much. I'm not a treasure hunter, and have never been metal detecting. That being said, I really respect this hobby/ profession on all levels. I live 3 or 4 hours from Oak Island on the US side and have been familiar with the story for around 15 years. I believe I've heard all of the plausible theories of who might have buried what, in the "money pit." I had heard rumors of Dan Blankenship's theory, which is close to mine, but had not heard it directly from him. I probably should have put this in the, "Bizarre, Strange, etc" thread about Oak Island, but since it was being discussed here I though it would be fine. I would like to add that I am in no way, shape or form an expert, or even an amateur. I have no education past a public high-school level. I have no documentation, or evidence in hand to prove my theory. I just like the Oak Island story, and spend way too much time thinking about it. And when I think about it, I like to imagine great things, not empty holes.
First I'd like to cover the skeptics side.
1. I know there is a widely-believed theory that the pit is a natural sink-hole, perhaps caused by a cave-in of the anhydrite. I believe the discoverers did find log platforms every 10 feet or so. I believe the Leginas found wood (And possibly concrete) in core samples last year, and in last night's episode. I believe men put the wood there.
2. I know of the theory of "pranks" that the Freemason's do. This conspiracy is traced back well into the Roman Empire. Almost every single Mason's "prank" I have heard of involves literally no manual labor. I have heard the Beale Cyphers are a Mason's "prank." This would make sense to me because no physical labor is needed to pull it off. I happen to have a manual labor job, and I would never join a club who makes its initiates dig a 5-foot hole, let alone a 90+ foot hole. Why not make them shingle your roof while they are at it. Maybe plow the fields, too. That's just me.
Now to my hole-filled theory.

Long-story, short. (Just from recollection and quick google serches. Feel free to correct anything.) Hernan Cortez, and his second-cousin, Francisco Pizarro were basically the financiers of the New World for Spain. Cortez handled all monetary issues in Cuba from 1511-1519. This included enslaving natives for his mines. Pizarro held the same authority in Panama City from 1519-1523. Then from 1519-1535, they undertake an all-out assault on South America. To my understanding Pizarro only returned to Spain a handful of times between 1519 and the time of his assassination in 1541. Cortez only returned to Spain in 1528 to contest that he had not withheld gold due to the Crown.
I believe these two men had every incentive and opportunity to amass an enormous treasure (over a relatively long period of time) and eventually formulate a plan to hide this treasure to try and ensure their family's future. The United States legacy is that the founders were tired of sending back the spoils of their hard labor to an unappreciative Crown. Why not Spanish Colonists as well? Surely they felt as though they could have matched military presence being that far away from Spain. I also find the tales of conquest curious. There always seemed to be such a small group (The Famous Thirteen) conquering these massive cities. Small groups are easier to pay off than big ones. Cortez ruining his ships. Finding El Dorado but not pursuing it for various reasons. Re-discovering it but it is in ruins.
To me, these two men fit every single aspect of the mystery. They are of the most famous explorers, so navigating to Nova Scotia would have been like driving to the in-laws to us. The earliest European settlement in the area was St. Croix in 1605. The Mi'kmaq were much less of a militaristic threat than they were used to in South America. Anyone looking to make settlements would most likely go where fruit the size basketball's grow, not where ice covers the ground 6 months a year. They were held accountable by no one as long as the king got his gold shipments. They owned slaves that were mining specialists. And the best part...They aren't Knights Templar.
Anyway, the theory is more detailed, but you get the point. I'm sure there is a smoking gun that explains why my theory isn't even remotely possible, but it drives me nuts that such a plausible sounding theory hasn't even been mentioned before. I apologize if someone else has stated this theory before. I swear I'm not ripping anyone off. I haven't even read any of the published books on Oak Island. I just read what I can find on the internet. So if you share this theory I'd love to hear more of what you think. I just couldn't believe that Blankenship thought it was the Incas, and not the Spanish.