Canada is a member of ICAO, as are most of the countries we host on this planet.
ICAO says all ATC communications shall be performed in English.
There is no wavering to that rule, what cloudrunner is saying is that everyone talking in English CANNOT degrade safety, while talking in French on the frequency at least slightly degrades safety, and in certain situations greatly affects safety.
Have a read up on one of Italys worst plane crashes
A contributing factor in the death of 118 people was that had the controller been speaking English to the Cessna jet, the SAS airplane might have understood that he was approaching the active runway.A report by Milan's public prosecutor said a "death trap" had been set at Linate.
The airport's ground radar system was out of service, even though the airport is frequently hit by fog.
Investigators also found that controllers had used Italian as well as the standard English to address the Cessna crew, and the crew was not asked to read back the tower's instructions.
There's a reason why ICAO has implemented an English competency by 2008 for all ANS operators and Airlines.
It's to the point now most foreign (to north america) airlines are rapidly hiring Canadians/Americans/Brits to fly for them specifically because of their excellent RT abilities.
When you have a "Asiana" or "Korean Air" pilot check in and his british accent is crisper than the London Fog, it tells you something about how important AIRLINES know it is to be able to communicate in English.