I have Sutherland ancestors who lived in Newmarket, Ontario also. Here is a quote from Jacob Gill Gaudaur's book, "The Place of the Fence." "...Commencing with the birth of Anna on November 15, 1801, five children were born to Sarah (nee Dunham) and Joseph Sutherland in Newmarket. The last four were Rachel born on November 29, 1803, Joel born February 1806, Lydia, born July 29, 1808, and Joseph Jr., born June 24, 1810."
Joseph and Sarah Dunham Sutherland relocated to the U.S. about 1812, plus or minus two years. Two daughters, my gg grandmother, Sarah Ann Sutherland and Anna remained in Newmarket. Sarah Sutherland married Jacob Gill and Anna Sutherland married James Dixon. Both couples lived in Ontario.
The Newmarket coincidence seems interesting to me, but I don't see where my Sutherland line connects with your Newmarket Sutherlands.