Instead of doing work I am supposed to do on my day off, I want to highlight my thoughts, both pro and con, about Gardiner removal:
PRO
A boulevard likely could meet capacity
The fact of the matter is that this is a surprisingly underused piece of infrastructure, and a large avenue could likely handle the traffic volumes placed on it.
Money saved
$200 million per year to keep such an underused stretch of road is a bit of a waste, when it can be used for so many other infrastructure purposes. Road resurfacing, bus lanes, THCH housing, rail transit expansion, etc.
Transit seems to be adequate
Likely the reason why it is used so little is because there is enough transit to divert demand from the highway. We have the subway and relatively frequent GO trains moving people providing service into lower downtown. And during rush hour, GO trains also run into northern inner and middle suburbs as well.
CON
Do network benefits outweigh demand?
Yes an avenue could likely handle demand, however, Toronto planners and amateur planners seem to have an obsession of fitting demand and capacity perfectly. While we should attempt to meet travel demand with adequate transport infrastructure, it will not always fit perfectly and neatly along every stretch of a corridor. There are rural stretches of the 401 which are likely overbuilt, are we dismantling it because of this? Network plays just as important a role as meeting demand. Yes this stretch of highway is underused, but it does play a role in creating a networked ring road around the city. Most cities which have taken down stretches of highways had several highways nearby, so the effects on the network were negligible.
Transit seems to be adequate... for now
Transit seems to be getting the job done, but it is no question that it is bursting at the seems. Even with more frequent service on the GO Lakeshore and Markham lines, the Yonge line continues to be bursting at the seems, and will likely continue to do so with all the construction taking place around its stations. The Richmond Hill GO line is not going to get all day service, which is the route which follows the affected corridor the closest. Toronto is fast growing city, and we need all the infrastructure we can get.