Great Grandpa Pearson is the son of The Woodsman and father of Chris's Grandfather.
He is ATLEAST seven years old, as he was born prior to The Woodsman's disappearance and is his biological son. His exact age is unknown, but based on the shows drawing style he is likely under the age of 10 as tweens in the show are drawn differently. He is apparently only half Canadian, as his mother likely came from Europe.
He fled to America around 1920 or so along with his mother and adoptive father, and at some unknown point(likely around the time WW2 started) had a child that eventually became Chris's grandfather.