The Standards and Guidelines for the Conservation of historic places in Canada (2nd ed., 2010) state that new additions to an historic place should be (1) visually compatible with, (2) subordinate to, and (3) distinguishable from the historic place.
From certain angles, the new design meets these criteria but from others it does not. The key culprit is that it is not sufficiently subordinate to the current Chateau. This is especially evident in the view from Major Hill Park.
In my opinion, the idea of a glass addition meets (1) and (3). It should be scaled down in order to allow, from any angle, the Chateau to remain dominant.