Based on your extensive vists to any of those places!!
When I have been to New York, I admit, very few people are actually New Yorkers. But they aren't actually foreigners, they are people from other areas of the USA.
I have just found that London is officially the most linguistically diverse city in the world. Fact. So that adds weight to my theory. I also found out that UNESCO has never labelled any city the most culturally diverse, so no facts to back up any theories. However... Unlike most Americans, I have actually left the continent I was born on, and I do so several times a year.
I also found that the USA's most ethnically diverse city is Sequoia Way. Never heard of it, though.
Found these -
http://en.wikipedia.org/wiki/Demographics_of_Toronto
http://en.wikipedia.org/wiki/Ethnic_groups_in_London
Although this -
http://en.wikipedia.org/wiki/File:T...ble_minorities_population_characteristics.png - reflects better against London as it doesn't break Whites down any further, as it does above.
I'd say they are pretty similar.
But... Over the last 5 years with the free movement from the European Market, London's ethnicity has rapidly increased. These stats are from 2007. I assume Canada's immigration policy is stricter, and rightly so.
Did I put too much effort in?