In the early '80s we moved the ranks off the sleeves for Operational reasons. Officers were easily identifiable in the 'Field' by the placement of their rank on their epaulets. To keep the Enemy from picking out the officers and targeting them, we moved all our rank up to our shoulders. It lasted for a year or two, but due to the confussion, even amongst ourselves (People were now saluting Cpls), we moved our ranks back to their original locations. Today, due to the fact that our webbing and Tac Vests usually hid Officer slipons, we have adopted a universal location on the front (like we did with our Arctic Parkas) to display our rank. 2 CMBG standardized its slipon placement on the Tac Vest as on the upper, front left shoulder blade. In this way all our rank is found in one common location and harder for a sniper to differentiate between officers and NCMs. Unfortunately, from the rear we don't know who a person may be (and we will not likely see any rank placed there as the buttons would be very painful when wearing a ruck).
As an aside, Canada is not the only country to locate it's ranks on the front.