Here is a page from the Wellington County Archives Tweedsmuir Histories
that mentions several Longman members landowners which may be of interest. https://www.wellington.ca/en/discover/mus-tweedsmuir.aspx
A page with Samuel Longman's name indicates he was a member of John Longman's family. John purchased lot 14 east half, Con 9 (Alma/Peel Twp) in 1856. This "Samuel" could be a nephew of the Samuel you are seeking?