Our family has a Mary Dutcher born in Canada in about that time frame.
This Mary Dutcher was born near Frederictonn New Brunswick, Canada in 1798. We think she was initially married to a John Horton, but after she was married she just seems to have disapeared from Canadian records. Perhaps John Horton died and she moved to the US and married your John Furman.
Mary's parents were John Dutcher and Ann Horton, M. 1790, who initially lived near Frederickton, New Brunswick, Canada after moving from the Tarytown/Rye areas of New York in about 1783.
We think John Dutcher parents were Barent Dutcher and Janetji Bracker of New York.
Ross Dutcher North Vancouver, British Columbia Canada