I don't think my paternal grandfather was in the WWI, he would have just been old enough at the end. He would have been too old in WWII but again there are pictures of him in a uniform at Camp Borden, so I am thinking probably Home Guard.
My maternal grandfather was a farmer which would have been considered essential service. However my maternal grandmother was in Scotland during WWI and worked in a munitions factory, she ended her service as an overlooker.
My husband's father was blind in one eye and never served, but two of his brothers served one was a Bombardier RCA, I don't know what the other one did and neither one would talk about their service.
Before that there are several ancestors who fought in the War of 1812, The Penninsular War, and one at Waterloo, and last one known U.E. Loyalist.
Janet