In a technical sense, it is true that all crown corporations are subject to various limits, beyond which they have to ask for Treasury Board approval
In my experience, the typical practice is for crown corporations to make their case, with all the details. That means that no decisions are made in advance. The Treasury Board or the Governor in Council should actually consider all aspects, including the political ones, not just the finances. For example, if the City of Montreal were to decide that a project of that kind was not acceptable because of municipal regulations, that is the kind of thing that the Treasury Board could consider.
So that is so for every case over $4 million. The request has to be submitted to Treasury Board, but normally that is not done before all the facts and the considerations have been gathered.