^ I'm guessing this is post-1981 if CF's tower was indeed completed in that year. Royal Bank Plaza (south tower) was completed in 1979 (north was completed in 1976) so your 1976-1978 guess may be a bit early.
@ brian"why why zed"
I can happily report the following to after forensic examination:
1. The drawing was completed on December 2, 1982.
2. The drawing was matted* and framed at a U-Frame-It store in the north/eastern city of Scarborough on January 28, 1983.
* the artist chose an inexpensive off-the shelf matte (mat) instead of an acid-free matte, resulting in the present discolouration you see. Suggest you consult a legal representative in regards to any possible action against the artist (38 years of intere$t due might be pursued for said discolouration).