I'm sure I'll regret asking, but what is a borough mayor? The idea of having an overall mayor and a bunch of little area mayors sounds insane.
Most merged cities have them, it's just than the other cities have the borough council elect it from their own members.
It's a two layers system.
City: Montreal mayor + borough mayors + city councillors. It manages city-wide issues
Borough: Borough mayor (Ville-Marie borough mayor is Montreal mayor) + city councillors from the borough (some small boroughs have no city councillors as they are entitled one seat in City Council, so only the borough mayor sits on City Council) + borough councillors (for small boroughs, so there is more than 2 or 3 members on it). It manages proximity issues.
It's quite a decentralised system. I think it's more democratic than most cities (i.e. Etobicoke forcing Rob Ford on central Toronto).
Etobicoke has about 13.3% of the population, hardly enough to have an influence on the rest of Toronto. In fact, the Downtown, on a per capita and representative basis, essentially makes the decision for the entire cities, and is probably the reason why places like Humber Bay don't have rapid transit.
