Questions regarding Passenger List of soliers returning from WW1

My grandfather returned to Canada in March of 1918 on the ship Canada. The passenger manifest lists are headed "Nominal Roll of Men to be Discharged in Canada".

Information on the manifest is as follows:
Reserve Unit: 3CCD
Military District: CE
Classification: B3
Reason for Discharge: Dis. Of A.G.

His rank was Spr (Sapper). But I'd like to know the full names of all the acronyms used in the listing.

Many thanks for your help.