Those were the thresholds that were set as part of international negotiations. I would add that this $312 million clearly, by law, applies to WTO countries. Non-WTO countries have a lower threshold prescribed in law, which is $5 million for direct acquisitions.
Evidence of meeting #32 for Industry, Science and Technology in the 40th Parliament, 2nd session. (The original version is on Parliament’s site, as are the minutes.) The winning word was nortel.
A recording is available from Parliament.