I have been working quite hard on this scenario lately.
The more I read about the history during this age, the more interesting it is I found. I would say playing most of the nations in this scenario will have quite a unique experience. I shall write some description of the nations here before I forget what I have encompassed

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Britain: ~70 cities. Greatest naval power on Earth, yet there are many challenges. You have Canada and Australia yet to be populated. Your colonies are everywhere on earth meaning your problems are also everywhere. Indian rebellions, Boers, Zulus and many other "barbarians" are all enemies of yours. You are also at war with China.
France: ~25 cities. Second to Britain. Have the largest army. You are about to invade Mexico and are expanding your colonies in Africa and Indochina. You are also at war with China.
Russia: ~50 cities. Invading Turkestan. Still possess Alaska. Technology is relatively behind.
Austria: 8 cities. One of the great powers. Technology is relatively behind.
Prussia: 7 cities. Unifying Germany. In the north, Hamburg is under the control of Denmark; in the south, Stuttgart and Munich are still independent.
Italy: 4 cities. Unifying Italy. In the north, Venice is under the control of Austria; in the south, Nepal and Palermo are still independent.
Spain: ~20 cities. Still possess Philippines, Cuba and quite a few islands around the globe. Technology is relatively behind.
Portugal: 14 cities. Have a lot of fragmented colonies. Technology is relatively behind.
Netherlands: 13 cities. Mainly colonizing Indonesia.
Denmark: 7 cities. The smallest colonial powers. Yet, it still possess a city in west Africa and another in Caribbeans.
Ottoman: ~25 cities. Have Egypt as a vassal. Some trouble arises from Arab as a rebellion force. Technology is behind the west.
China: ~45 cities. If including the cities under rebellion, you are the most populous nation on Earth. You also have Joseon as a vassal. Most of your time and effort will be fighting the Taiping and many other rebellions from all around your territories. Britain and France have also declared war on you (Second Opium War). Technology is way behind the west.
Japan: ~6 cities. Meiji reformation has just started. Two cities in the north are still independent. Technology is way behind the west.
United States: ~15 cities. Fighting the Civil Wars with the Confederacy and at the same time, the Sioux in the wild west. Adopted Emancipation, Free Speech and Free Religion.
Confederate States: ~8 cities. Adopted Slavery.
Morocco, Arabia, Siam, Sokoto, Abyssinia, Zulu and Sioux: 3-5 cities. Technology is way way behind the west. Almost hopelessly waiting for slaughter. Yet, if you are looking for challenges, this will be it. They will start out with a significant number of army so that they won't be destroyed too easily at the beginning.
To be continue...