If you want cities that are similar in size and density to Toronto:
Guadalajara Mexico 3,500,000 metro 5,900 people per sq km
Athens Greece 3,685,000 metro 5,400 people per sq km
Madrid Spain 4,900,000 metro 5,200 people per sq km
Barcelona Spain 3,900,000 metro 4,850 people per sq km
Belo Horizonte Brazil 4,000,000 metro 4,600 people per sq km
Berlin Germany 3,675,000 metro 3,750 people per sq km
Riyadh Saudi Arabia 4,000,000 metro 3,650 people per sq km
Kuala Lumpur Malaysia 4,400,000 metro 2,750 people per sq km
Milan Italy 4,250,000 metro 2,750 people per sq km
Toronto Canada 4,367,000 metro 2,650 people per sq km
Sydney Australia 3,502,000 metro 2,100 people per sq km
Miami USA 4,919,000 metro 1,700 people per sq km