Useful population keywords might include:
Note that the asterisk at the end of a term will search for singular and plural word forms. You might combine your population keywords with geographic location terms, such as Canada or British Columbia.
Many databases have subject headings you can use in your search to find more relevant results. For instance, there is a MeSH term in PubMed / Ovid Medline, "Indians, North American." Please be aware that often the subject headings in databases use outdated and potentially offensive terminology.