Complex sentence: Cape Breton Island's first residents were likely Archaic maritime natives, ancestors of the Mi'kmaq, who inhabited the island (known as Unama'ki) for several thousand years and continue to live there to this day.
Split into simpler sentences: Cape Breton Island's first residents were likely Archaic maritime natives, ancestors of the Mi'kmaq. These peoples and their progeny inhabited the island (known as Unama'ki) for several thousand years and continue to live there to this day.