This question comes up often, and it stems from the confusion over the distinction between "The Crown," as it was historically interpreted, compared to how it's legally evolved in modern-day Canada. 

Yes, there's no doubt that the monarch may have a symbolic or cultural connection with Indigenous peoples. However, the legal relationship they have (i.e. treaties) is not with the family of those in whose name those treaties were signed, it's with the contemporary Canadian Crown, as defined by the Letters Patent 1947, which delegated powers of the monarch from King George VI to the Office of the Governor General.

Thus, the Letters Patent began the process of interpreting the Canadian Crown or Crown in Right of Canada as the Canadian State, not the monarchy - or individual members of the royal family.

Even "The Queen," in its legal sense, has been upheld by the Ontario Superior Court as not the person, but the abstract entity synonymous with our form of government: the Canadian State.

• "In this case, however, the appellants’ claim of adverse effect is based on their misconception of the meaning of the oath to the Queen as an individual. Earlier in these reasons, I quoted the words of Laskin, at pp. 119-120, that viewing “Her Majesty the Queen” as an individual was an anachronism and held that the reference to the Queen in the oath was a reference to our form of government." McAteer v Canada 2014

Thus, the monarch (now King Charles III) personally has no effective power that can be applied in any jurisdiction (including treaties) without it first being approved and/or directed by our government. To do so without it, would cause a constitutional crisis many times eclipsing Canada's King-Byng Affair or Australia's Dismissal Crisis of 1975.

Of course, it doesn't help when monarchists continue to mislead Canadians by claiming that becoming a republic means "abolishing the Crown in Canada,"  or that it would throw our legal system into disarray, or that it would nullify Indigenous treaties. 

Based on that kind of misinformation, no wonder Indigenous people worry about their treaties. If all they've been told is that they were signed in the name of the Crown, and the Crown will disappear when we become a republic, logically, they'll be against change.

Outrageous claims like that have just one purpose: to muddy the waters and confuse the public in order to protect the status quo. CCR has known about these tactics for a long time. That is, after all, why our organization was founded.

If those assertions were true (abolishing The State), Canada itself would cease to exist, and we know that won't happen because Ireland, India, and most recently, Barbados became parliamentary republics, and not only did their "State" survive just fine, their legal obligations to international treaties continued seamlessly.

But are, "international" treaties the same as Canada's treaties with its Indigenous Peoples? 

According to Crown-Indigenous Relations and Northern Affairs Canada, treaty and Indigenous rights are recognized and affirmed in Section 35 of the Constitution Act, 1982. 

But they're also covered under international law as part of the United Nations Declaration on the Rights of Indigenous Peoples which the Government of Canada has committed to adhere to in BILL C-15 - An Act respecting the United Nations Declaration on the Rights of Indigenous Peoples.

Notably, Bill C-15 states: "The Government of Canada is committed to achieving reconciliation with Indigenous peoples through a renewed, nation-to-nation, government-to-government, and Inuit-Crown relationship based on recognition of rights, respect, co-operation, and partnership as the foundation for transformative change."

Therefore, a violation of treaty rights by Canada is a violation of international law. And just like Ireland, India, Barbados or any other post-monarchy state, upon becoming a republic, Canada is obligated both by its own laws and international law to continue its treaties.

 Many Indigenous constitutional experts themselves have confirmed that treaties signed with the Crown decades or even centuries ago, are now the jurisdiction of the Canadian government, not the reigning monarch.

Some of them are even prominent members of the Indigenous community:

•  “[The Royal Proclamation of King George III and Treaty of Niagara] establish a clear relationship between First Nations and the Crown (now Canada) and a protocol for Treaty-making between both parties where lands and resources were to be shared.” -
  Shawn A-in-chut Atleo, former National Chief of the Assembly of First Nations, The Globe and Mail, Oct 7, 2013
  
  
• "the Crown in right of Canada now holds the legal responsibility for honouring, implementing and enforcing the Treaty provisions." - Perry Bellegarde, former National Chief of the Assembly of First Nations. Ottawa Citizen, May 01, 2023
  
  
• "My perspective is that the duties that ensued from the treaties have been taken over by the Crown in right of Canada and the Crown in right of the different provinces. And so if there was a republic, the duties required to ensure that this country [honours treaties] between the original Great Britain pre-Confederation would continue." - Delia Opekokew, lawyer with a specialization in Indigenous treaty rights and Aboriginal Law, member of the Canoe Lake Cree First Nation, former Deputy Chief Adjudicator - Indian Residential Schools Settlement Agreement (IRSSA), former vice-president of the Canadian Civil Liberties Association TVO, Oct 29, 2020

• “The absence of this queen is not going to negate the government's responsibilities to their treaty relationships and their relationships to indigenous peoples.”
  Jordan Gray, policy analyst with Indigenous Affairs Canada, CBC News, May 15, 2022

• “after 1867, the Government of Canada assumed all control over Indigenous affairs, including the signing of treaties with First Nations. The Crown is the legal name for the British and later Canadian governments: federal and provincial.” Jennifer Cooper, spokesperson for Crown-Indigenous Relations and Northern Affairs Canada, Chatelaine Magazine, 'Should Canada Finally Abolish The Monarchy?' June 29, 2022

• "There have been and probably are First Nations leaders who would like to be dealing with a remote Imperial Crown rather than with the settler government of Canada, but the imperial responsibility for aboriginal matters was long since transferred to the Canadian state, and the Queen is not going to (indeed, could not) overturn that reality under any circumstances. That issue has been gone a very long time." - Christopher Moore, historian, author of books on Canadian history and law, two-time recipient of the Governor General's Literary Award, "Abolishing the monarchy -- what, like it's hard?" christophermoore.ca

The Queen herself has confirmed that legal relationship, for example in 1973, when she reassured Chiefs in Alberta that the Government of Canada "recognizes the importance of full compliance with the spirit of your Treaties."

Consequently, all grievance letters to the Queen regarding treaty rights are politely accepted and then forwarded back to Canada.

Even letters personally accepted by members of the royal family during visits to Canada, are promptly handed over to a representative of the Canadian government, as was documented by the media in both 1994 and 1997.

And very importantly, since 1982, all indigenous rights, including those as expressed in the Royal Proclamation, are not just protected under Section 35 of the Constitution Act, but also Section 25 of the Charter of Rights and Freedoms.

• Thanks for the enquiry, but this is a matter for the Canadian Government.”
  Donal McCabe, communications secretary to the Queen, January 27, 2021, when answering a letter from the Confederacy of Treaty Six First Nations, asking the Queen to encourage Canada to consult Treaty nations before appointing a new Governor General to replace the outgoing Julie Payette.

Therefore, all legal matters relating to the Royal Proclamation of 1763, or any other pre or post-Confederation treaties, are between Indigenous people and the Government of Canada, and will not change for the worse if we choose to have a non-monarchical head of state.