I think this practice depends very much on the Regiment. During my Militia service in Toronto 1974-1982, IIRC the Pioneers and Skirmishers of the Queen's Own Rifles normally preceded the Drums and Bugles, the Band, and the main body. Although I know that the Royal Winnipeg Rifles do it, I wonder about the historical accuracy of the Pioneers "protecting the Drums" since traditionally the place of Pioneers in a column of march was well out in front of everybody, clearing the route.
Cheers