Are their mixed marriags all over Canada and the US yes...BUT the question was "Is there an earliest date for Metis", so in my way of thinking ...my answer was directed at the Actual Original Organization(s) of the Metis Cultures to come together and ALIGN as Actual METIS Nation(s), which did infact occur with the RedRiver and Louis Riel & the Government of Assiniboia & with Saskatchewan , If someone is Genealogically trying to Locate records of these Metis, the Scrips are listed as such for NWT(Northwest Territories & Prairies). In Quebec and NS the Records are NOT listed as such(if they have a bunch of em hidden in boxes somewhere I've not found em in the BAnQ searches yet., so to say that they are there in Quebec & NC is true, but finding them is not as simple as searching for the: "Metis" in Quebec or PEI or NS or many other areas because they were not listed as "Metis" in the docs if they were...its is very rare-few-and-far between.
And one more thing about NS, I just came across an old pic in the NS Museum and Archives, that includes I think like 34 individuals all or almost all dressed in Traditional Mi'Kmaq Regalia.These people included some Pitre/Peters Family members, which are known to have french roots as well as n8v, but they aren't dressed as Metis, they are dressed as Mi'Kmaq. This says to me that those or at least some of those that lived near thier n8v relatives were inclinded to be an actual part of their Native Nations acknowledging themselves as (like the ones in the pic-as Mi'Kmaq and being acknowledged as such by their counterpart "full-blood' family and friends. Nowhere on this photo are they called Metis...just as in the records either their Nations are listed or some "ja" just called em "indien, sauvage, vagabond, bois-brule, malange, melungeons, and many other derogatory terms just wanted to clarify.
& My answer was based on the question. Theres' a whole lot of history to how the original Metis Nation came about, but putting it all in here to answer this question certainly didn't seem to be the answer to the question. just sayin