Have hit a brick wall with this pair - 1881 census shows they were living in Winnipeg (continued on to Saskatchewan in 1882 where they settled), but family lore says Sarah was born in Glengarry (1832), and Alexander at Loch Tay Scotland (1833). Alexander passed away in 1913 and Sarah in 1919.
They had seven children:
Finlay A. McPherson (1857) married Ester McCarger
Christina McLeod (1856)
William McPherson (1862-1927)
Catherine McMunn (1864)
John McPherson (Jack) (1863) married Marjory McDougall
Alexander McPherson (1873) married Ethel
Hector McPherson (1875-1952) married Mary Caroline Craig
The birthdates for all but Hector (my g-grandpa) were guesstimated from the census...