Quebec historically clings to the argument that an unofficial agreement in general between the Atlantic provinces and itself settled the boundary issue in 1964 - the so-called Stanfield Line. Newfoundland and Labrador has always challenged that boundary stating that not only was it general in terms, but that it was not ratified by an Act of Parliament as would be required under the Constitution. In actuality, the 1964 agreement was more an effort by the provinces to secure sub sea minerals (oil and gas) for themselves. The boundary issue was loosely agreed to in connection with this strategy. In 1967 the Supreme Court of Canada, in a constitutional reference on the matter, found that the seabed belonged to the federal government.
In 2001, Newfoundland and Labrador and the Province of Nova Scotia went to arbitration in order to establish the validity, or lack thereof, of the 1964 Stanfield Line agreement. The following is the finding of that group:
For the forgoing reasons, the Tribunal unanimously determines that the line dividing the respective
offshore areas of the Province of Newfoundland and Labrador and the Province of Nova Scotia
has not been resolved by this agreement.
Hon. Gerard La Forest
James Richard Crawford
In other words, there is no agreement upon which any maritime boundaries could be established or recognized.
The old 1964 agreement had an administration line that essentially brought Quebec's maritime border all the way from the mouth of the St Lawrence to 80 kms east of the Magdelen Islands - a massive 350 kms or so. Without such an extension to encompass a tiny set of islands Quebec's maritime boundary would not surpass 50 km east of Anticosti Island into the Gulf. In reality, the Magdelen Islands actually lie more in Nova Scotia's waters than they do in Quebec's. There have been legal precedents set for small islands lying off the waters of another's jurisdiction, and not conforming to the natural coast line of the host jurisdiction. One in particular case, St Pierre and Miquelon Islands (France), is a very good example.
St Pierre and Miquelon Islands are the last territorial remnants of France's once great empire in North America - located just south of Newfoundland. In fact they are so close they are located within Canada's Exclusive Economic Zone (EEZ). Canada and France had been squabbling for many years over the territorial waters that such an island deserved, and the effects on Canada's EEZ. In 1992 it was finally submitted for binding arbitration with three neutral international panelists, and one each from Canada and France. In a three to two decision, the two being Canada and France, the committee decided that France kept a 22.5 km territorial sea surrounding the islands and an additional 22.5 km contiguous zone. It was only 18% of the claim that France had made. The remainder of the territory was to remain Canada's EEZ, with the exception of a small corridor to the open seas. The committee used a straight forward interpretation of the Convention on the Law of the Sea, which Canada was a signatory to.
Based on this very close example, The Magdelen Islands would only have a very small "territorial sea" surrounding them, and not essentially the entire Gulf of the St Lawrence. Quebec's "administration line" or maritime boundary would then stretch in a line following it's mainland coast, but encompassing Anticosti Island. The result of this alignment is that Old Harry is not actually situated in Quebec's maritime economic zone. Far from it. The same territorial sea argument can likely be made for Anticosti Island as well.
According to the Constitution, boundary changes between provinces themselves must be agreed upon by those provinces involved and then sent to the federal government for ratification. The federal government can arbitrate, but only if requested to do so by the affected provinces. Without a settlement of the boundary issue Quebec cannot form a joint board with the federal government to oversee and grant licences for offshore exploration and development. It is highly doubtful that Newfoundland and Labrador would subject themselves to that process. Although, if they did, precedents seem to indicate that Quebec would lose and Old Harry would belong to Newfoundland and Labrador. However, should Quebec continue to cut it's nose off to spite it's face, Newfoundland and Labrador might as well develop the east side of Old Harry and, as they say, oil has no borders.
What should be:
The 1964 Stanfield Line: