Max Méndez Beck phrased it this way:

what do you think is the most multicultural (minimal segregation while having great ethnic diversity) city in the world?

Toronto springs to mind as a candidate, but it is increasingly expensive and perhaps more ethnically segregated than it used to be or at least more segregated by income and class. Montreal is gaining on it by this metric. Sydney is likely in the top ten, but too many parts are posh to be #1. Sao Paulo has so many ethnicities, but when you get right down to it they are all Brazilians. Don’t laugh, but Geneva might be in the running, both because of immigrants crowded near the center and the city’s international organizations. But perhaps I will settle on Brooklyn, which if it were its own city would be the fourth largest in the United States. (I love Queens, but have a harder time calling it a city.) Brooklyn has recent arrivals from almost the entire world, and even the very nicest of neighborhoods are usually not so far from the poorer areas. Still, if you refuse to count Brooklyn, it is striking that Montreal has a real chance of topping this list: wealthy enough to bring in foreigners, not so wealthy as to price them away.