Accent. Apparently people from the Prairie Provinces of Canada (like Manitoba) don’t really have an accent and DB Cooper was described as having no accent which eliminates Quebec as that has a prominent accent and that could extend to Ontario, British Columbia and Yukon. Also people described him as appearing to have indigenous or Latino ancestry. My best guess is he is Metis who are commonly found in Manitoba (the man credited with establishing Manitoba was Metis, Louis Riel). Of course he could be from Alberta but my suspicion is that he tried to pass as being of Italian heritage and Winnipeg has a large Italian Canadian population (not sure about Alberta) so I think he spent time in Winnipeg. Honestly this was based on research I did years ago.