For as long as I can remember, this building has been referred to as the “comfort station”.
I recently learned it is listed as the “pavilion” in Canada’s Historic Places. In fact, the building and the entire park are listed as a historic site.
http://www.historicplaces.ca/en/rep-reg/image-image.aspx?id=19610#i3
‘Westmount Park (1898-1899) and its pavilion (1929, MacDougall)”