Anyway, since you asked.......
The term comes from the mid-19th century "Clear Grit" party, who were Upper Canadian reformers with support concentrated among southwestern Ontario farmers, who were frustrated and disillusioned by the 1849 Reform government of Robert Baldwin and Louis-Hippolyte Lafontaine's lack of radicalism.
The Clear Grits advocated universal male suffrage, representation by population, democratic institutions and free trade with the United States. They came under the leadership of Toronto editor George Brown and, in 1857 joined with the Reform Party to became part of what became the Liberal Party of Ontario and Liberal Party of Canada.
The Clear Grits were one of a long series of farmer based radical reform movements. Later examples were the United Farmers and the Co-operative Commonwealth Federation. The word "Grit" has become synonymous with "Liberal" in English Canada.
My, how things change, eh?