Not to knock CIBC Square, but most of the extraordinary exterior magic comes down to glass cladding (and angles)... perhaps the best I've seen anywhere on a new building.
But using the cladding metric, RBC Plaza, completed over 40 years ago, remains in my estimation to be the most beautifully clad project on planet earth. Rarely discussed in geek forums, but the serrated gold twins are still simply the best dressed scrapers anywhere (and certainly no other "Fools Gold" imitations have matched it ;-)