I'm not in favor of burying the gardiner either, and I think with the right planning and infrastructure there could be a day where we could tear it down - but that day is not today, and will not be for the next 20 years.
You want to know what alternatives drivers will find? They will drive on King, and Queen, and Front, and Richmond, and Adelaide. And they will be frustrated, and there will be more accidents, and streetcars will run slower. What they *wont* do is magically decide to take the GO train or TTC.