The largest installation of mercury vapour streetlights that I know of is about is 12-15 mercury vapour Sylvania Powerlite B2255 cobraheads in a subway drop off area. I would like to imagine that somewhere in Ontario MV is still used for streetlighting.

This and I think this on the Toronto section of Highway 401 used to a very large installation of mercury before the great changeover to HPS during the late 1980's and early 1990's