Things They Should Invent: tournament-style mayoral debates

In this past election, Toronto had a ridiculous number of mayoral candidates and a ridiculous number of mayoral debates.

But, for the vast majority of debates, only the handful of candidates deemed "mainstream" by the media are invited, with the dozens and dozens of others being completely ignored.

This is a waste of perfectly good scheduled debate time!  What's the point of having such a ridiculous number of debates if you aren't going to host all the candidates?

Therefore, I propose tournament style mayoral debates.  During the first few months, candidates debate each other in a round robin sort of format, so as many people as possible debate as many people as possible.  Then the people who have won the most debates move on to debate the other people who have won the most debates, until the top debates in the city are facing each other towards the end of the election period.

I'm picturing a sort of World Cup format for this, but it wouldn't be exactly the same because debates most often have more than 2 people.  And a true round robin might not be possible, depending on the math.  But, in any case, they should do whatever most convenient mathematically and scheduling-wise to get as many people as possible to debate as many people as possible.

So how do we determine who won a particular debate and gets to move on in the debate-offs?  My first thought is an audience vote - perhaps just in person, perhaps both in person and online.  But I don't know if that could be over-influenced by candidates stacking the audience. 

Another idea is a panel of judges.   But would they assess the candidates objectively, or would they favour the big names?  Although, the existing system already favours the big names, so could it be any worse?

What if audience members are assigned tickets to a debate, but they don't know who's going to be debating at the time they sign up for tickets (which would make it impossible to stack the audience).  But would enough people actually go to debates where they don't know who's debating?

Another alternative would be not to vote on winners of individual debates.  Candidates round-robin, the videos are posted online, and online viewers can vote for which candidates they'd like to see debate some more.  But, again, how could we prevent candidates from stacking the votes?

I haven't fully worked this out.  But the fact remains: if we must have dozens of candidates and dozens of debates, all candidates should get to debate.