Maybe one of these is the right Joh Mcnab who died between 1868 and 1872.
John Mcnab
Ireland Civil Registration Indexes, 1845-1958
birth: 1811
death: 1871 Claremorris, Ireland
John Mcnab
England and Wales Death Registration Index 1837-2007
birth: 1829
death: 1870 Wigan, Lancashire, England
John Mcnab
Ontario, Toronto Trust Cemeteries, 1826-1989
birth: 1824 Canada
death: 11 April 1871 Canada
burial: Toronto, Ontario, Canada
John Mcnab
Ontario Deaths, 1869-1937 and Overseas Deaths, 1939-1947
birth: 1824 Canada
death: 11 April 1871 York, York, Ontario, Canada
John Mcnab
Nova Scotia Vital Records, 1763-1957
death: 1871 Halifax, Halifax, Nova Scotia, Canada
residence: 1871 Halifax, Halifax, Nova Scotia, Canada
John McNab
Find A Grave Index
death: 1871
burial: 1871 Durham, Grey County, Ontario, Canada
John McNAB
Find A Grave Index
death: 1871
burial: 1871 , , Argyll and Bute, Scotland
John Mcnab
Find A Grave Index
death: 11 April 1871
burial: 1871 Toronto, Toronto Municipality, Ontario, Canada
John McNab
Find A Grave Index
death: October 1871
burial: 1871 Forgan, , Fife, Scotland