I never hear both. I recall often hearing the bilingual version at high school and other public events: 2 lines English, 4 lines French, 3 lines English. In Toronto, it's usually the English version at baseball games. My guess is that at Quebec hockey games, it's the French version, but I've never been (and I don't watch hockey on TV). (Yes, you can be Canadian and avoid hockey.) What do they do in Belgium? What about Switzerland, which I believe is officially trilingual: French, Italian, and German? (Quadrilingual actually) Do they dispense with singing altogether? I would.
I don't really know, since I am Dutch, not Belgian. Belgium is also trilingual. French, Dutch and German. All three versions of the anthem say pretty much the same, so lines could be interchanged to form an trilingual version. According to Wikipedia, this is actually what happens at the national day, just like the bilingual version of O Canada. As for Switzerland. I honestly don't know. Maybe I'll ask my previous room mate. His girlfriend hails from Switzerland. I'll keep you posted.