It may be a reality you face, but if you can explore other options....
The question was put, what do you need for political legitimacy? You need the Canadian electorate to really believe and trust that this system will actually work. That's all you need. It's not a legal question, it's really a political question.
So I'm not sure you have to go to a referendum, but you'd have to explore other options. I wasn't very good at giving you any other suggestions, either.