Would seems we're both slightly off the mark; it's actually about 100k sq ft as per the
final planning report.
And thanks for the numbers. Even with Casa3 coming in slightly lower than I initially pegged it at, that still leaves the area with about 500k square feet of new space, which would be a net increase of 100-150k. It's hardly huge, but even so, it's definitely nice to know that we're nonetheless seeing an overall increase in space (and to have the numbers to validate that fact)!
Edit: And just to veer slightly further off topic, since we're on the subject, broadening things to look at the some of the other office developments that are occurring between the core and Bloor, there's still about
50k in Wellesley on the Park,
35k in Alter (which will be an increase over what's currently there, though not sure by how much), and
40k in the Oak Towers addition, plus the "partial 8th floor addition" to
800 Bay St (for whatever that's worth), and that small addition to Oddfellows Hall.
There's also the Ontario Government office building at 880 Bay, which will inevitably get built at some point, long a way off as that may be, nevermind Mars2's still relatively recent and massive 700k sq ft contribution.
By contrast, the only office space that's really been lost, as I can recall, would've been that medical office building on Wellesley East, where Vox is going up,
this one, that went down for 1001 Bay, and about a floor of office space above the retail at 460 Yonge, so overall, also a pretty good level of growth happening south of Bloor (but north of the core) as well.