It does remind me of the Chateau Laurier approach, and it seems to cover the bare brick area on the south side of the hotel.
It's not very tall, but I wonder if the base includes some office space for a CTV expansion to its space in the old Library?
That recess seems to inetgrate with the deck on the old library.
Here's a pic showing the extent of the brick on the south side (i.e. which an extension would cover up)
Looks like the addition just exceeds the 2nd setback, so well below the copper roof and maybe just below the Roof's arched windows.
https://www.insidevancouver.ca/2014/02/2...st-rooftop-bar-at-hotel-vancouver-opens/