From a large collection of glass stereoviews that belonged to Dr William Gardiner Anglin (1856 - 1934) who lectured at Queens University in Kingston, Ont. photo circa 1905
Titled "Old Cannon Westminster" though I suspect the photo was taken at the Tower of London as I have seen photos of the gun there from the 1920's
It's interesting to note the large number of guns and mortars stacked in the background, another indication that it was taken at the Tower.