Seems more likely that it was really a three-storey building and only the facade was kept when they consolidated various properties into the one-storey Staples.
Edit: I seem to be correct. I checked the historical photos on GeoOttawa, and it seems to have happened in the 90s.
1991:
1999:
PS: I have been in and past this building hundreds of times before but never really looked. The heritage facades are the only bits of the old buildings remaining; otherwise they were completely demolished, and replaced with a steel-frame big box store. It was a complete facadectomy.
Noticed that on Geo the other day as well. For what it's worth, they did do a pretty good job preserving the facade, but you can tell by the window's something's wrong. Kind of sad.