Let me check at the Uxbridge library for any information about the Brethours.
I did find the following in Scott Township in the 1861 Census. As you may know, Udora sits on the border between Scott and Georgina Townships. No way of knowing by this census where they were in Scott:
Brethaw, James, yeoman, b. Ireland, English Church, aged 36, married
Brethaw, Phebe, b. Canada, aged 30, married
Brethaw, Eliza, b. Canada, aged 10
Brethaw, Michael, b. Canada, aged 8
Brethaw, Samuel, b. Canada, aged 6
Brethaw, Katharine, b. Canada, aged 4
Phebe's death record in 1918:
Phoebe Brethour, died 5 June 1918, aged 87 years, 3 months, b. Brock Township, died Sunderland, burial in St. John's Cemetery, widow, daughter of Philip St. John & Ann Baker; informant: James Brethour of Sunderland.
Is this John in Trafalgar, Halton County in the 1851 census:
Brethour, John, farmer, b. Ireland, Episcopalian, aged 67, married
Brethour, Ann, b. Ireland, aged 60
Brethour, Edward, b. Ireland, aged 34
Brethour, Joseph, b. Ireland, aged 19
Brethour, Hannah, b. Ireland, aged 24
Another death of interest:
James E. Brethour, died January 2, 1929, aged 87 years, 4 months, 11 days; born 22 August 1841 Georgina Township, son of John Brethour, b. Ireland, and Eliza Shier, b. Ireland; informant: W.O. Webster, nephew, Udora; burial in St. John's Cemetery, Brock Township.