Don- I came across some interesting information on Alexander Weatherhead, the son of Samuel and Magdalene, some of which you may already know. There is an article called The First Tay Canal on the website for the Lanark County Genealogical Society which tells about Alexander starting to build a dam and construct a mill at Fishing Falls in 1829 without getting government approval and a long legal battle he had with the government. I also found Alexander Weatherhead settled about 1825-30 on Lot 1, Concession 5 of South Crosby Township along with his brother, William, your ancestor, and his brother-in-law, Terence Smythe, my ancestor. They were all part owners of the mill at Whitefish Falls, now Morton. By 1837 Alexander had moved to North Elmsley Township where he married Mary Pye and had 6 children, George Henry, William, Elizabeth who married William James McCue, Ann, James, Alexander and Samuel who married Agnes Ann Beckett.
I have also run across the birth records of William Weatherhead and Catherine McNabb's children, Samuel R. born November 8, 1836 and Andrew W. born August 20, 1838 in the birth records for St. Andrews Presbyterian Church in Perth. The Weatherhead's residence is listed as Elmsley. This is a coincidence because I have another unrelated Scottish branch of ancestors, who were also in the St. Andrews records for the 1830's, the McTavishs and the Robsons, who were living in Elmsley and Drummond.