This small set of photos depicts a boat parade on the Rideau Canal in May of 1977, presumably for the tulip festival. The photos were taken from alongside the Rideau Canal by the NAC, looking across the canal to the east side. Here, for example, is Union Station (now the Government Conference Centre):
A less prominent building was also photographed that day: Canada Post's Ottawa Station A (Station B is at Sparks & Elgin), located on a part of Besserer Street that's now buried under the Rideau Centre:
I haven't done any research beyond pulling up a couple of relevant incidental mentions from URBSite. The second photo in this URBSite post identifies the building with the following photo and caption:
"Here's a brief update on the Corry Block - from the CNR photo collection at the Museum of Science and Technology a view of Corry's back, the tip of the triangle. The building to the right of the smoke stack is Postal Station B (Cecil Burgess, 1933) which was demolished for the Rideau Centre."While the skyline in that photo looks filled with buildings, I was surprised by this one from my family's set showing a big gap looking North ("North-East" on Ottawa's street grid) between the Union Station building and the former postal terminal. You can also see that an unadorned three-floor addition was slapped onto the back of the building since the CNR photo was taken.
At the left of the gap you can see in the distance the top of the Union of Canada Life Insurance building, and in front of that you can just make out the cornice of a building. Based on the sightlines, I suspect it's J.R. Booth's Transportation Building, though the cornice doesn't look right compared to other photos of that corner. This URBSite post on the Corry block includes an aerial view that shows the building, and the former road configuration at the West end of Besserer, though it doesn't give any definitive clues on the cornice.
The photographer was paying attention to the parade and not the buildings behind it, but fortunately for us, these clowns drew the lens up to give us an excellent view of the top of the building.
*Having been out of town for a couple of weeks, I've fallen behind organizing my photos of Ottawa, as well as the many I've taken upon my return to catch up on progress on various sites. As a result, I'm behind in my blogging, so pardon the occasional missed post while I catch up on things. I might have to grab another '70s family album photo or two to fill in the gaps here and there.