We had a referendum. It was called the General Election. Four parties (Liberal, NDP, Bloc, Green) all had electoral reform as a leading part of their platform. Every vote for any of those parties implicitly accepts reform.
A referendum is just a way to so ignorance and allow the parties that benefit from the status quo to continue doing so.
By your logic, every single bill that comes before the House needs to be put to a referendum.
Nobody would claim that our general election was a referendum on our electoral system. Every party has a platform, nobody agrees with everything nor does winning an election provide the winning party the right to fundamentally change our electoral system based on a minor election promise. Heck, the Liberals promised $10 B deficits, so much for that one.
A referendum would allow for broad based public support of the new system. In the event that a significant proportion of the electorate disagrees with selected new system, or views it to be bias towards the incumbent party, then many Canadians will not deem the outcome to be 'legitimate'. What happens if Quebec voters deem the new system to work against them ? Watch seperation take on a life of it's own.
No, ever single bill does not need to be put to a referendum, that is a poor logical leep on your side. Something that fundamentally changes the foundation of our democracy, a democracy that relies upon the trust our citizens put in it, has to be widely accepted as legitimate. Only way to do that is with a referendum.