Treasured for its necessarily broad scope as well as general anglophilism in the TW community, Great Britain is probably one of the most played factions in the Grand Campaign. It's undeniably a great deal of fun: not only does it have the most unique units in its roster by default, it also benefits by far the most from the DLCs, with numerous special infantry and cavalry regiments, and even a unique ship.
Great Britain has probably the most ambitious Grand Campaign. Not only does it have to acquire large tracts of the Americas, it also needs to take a sizable portion of India, as well as random spots in Europe such as Gibraltar and Egypt. This leads it to conflict with nations from France to the Cherokee Nations to the Maratha Confederacy.
Great Britain has to juggle many issues with limited resources. A substantial portion of its income is from trade, so it must have a strong navy to fight off Pirates, France, and Spain. While it initially has the best fleet and can defeat any other single opponent, Great Britain may find itself overwhelmed by sheer numbers if it is not careful in maintaining its fleet. Containing the Pirates early while establishing trade can pay handsomely, and allows for easy expansion without incurring the wrath of other factions.
France, Spain and their allies are major threats in both Europe and the Americas. Their fleets are individually almost as formidable as Great Britain’s, and will actively patrol trade routes. It is possible to knock France out early by trading Scotland for Alsace-Lorraine and then taking Paris by storm, but this feels a little like cheating. French and Spanish holdings in America are vast, that is true, but they’re generally poorly defended—just a couple of well-equipped armies should be able to comfortably evict the Bourbons and Hapsburgs from the Americas.
The Native Americans are another matter. They field large armies that are deadly in a melee (particularly in the early game where bayonets are unavailable), and their bowmen can cause headaches for early armies that lack skirmishers. British Colonial Line Infantry are significantly worse than their European counterparts, so bringing over troops by ship may be wise. Hessians may be trained in the Americas, too, and while they aren’t as good as line infantry, they are much better than militia and can be just as ubiquitously trained. Native auxiliaries can provide much-needed cavalry, skirmishing, and melee support. If the player has the various DLCs installed, Great Britain also has access to some excellent light infantry and cavalry in the Americas.
Fighting off the French and Native Americans grants the prize of the Thirteen Colonies. While vast, their lands are usually very underdeveloped when you acquire them, so plan to invest heavily in the region before seeing meaningful returns.
With mastery of the seas and a stabilized situation in America, seeking the Indian sub-continent before the Marathas solidify their control there is a wise move. The Indian factions should prove no match to veteran armies from the Americas and Europe. It’s not a bad idea to simply take all of India: not many other factions can do much about it, and much trade revenue can be obtained from selling the goods there.
The European theatre presents unique challenges for Great Britain. Amphibious invasions will have to deal with the often-numerous armies of both France and Spain. Great Britain’s objectives include Gibraltar (initially controlled by Spain) and Egypt (controlled by the Ottoman Empire). Simply destroying France and Spain to obtain Gibraltar could be a good idea—they are thorns in your side that will essentially never go away unless wiped off the map. One could try negotiating with the Ottomans for Egypt, as defeating them in detail could be tricky considering the vast size of their empire.
This one's a doozy to get through. CA clearly showed their favoritism in roster design, and it's nowhere more obvious than here.
Let's get the easy stuff out of the way first: the artillery roster is standard. And...that's it. Nothing else is easy.
GB's navy has unique stats. It has much better reloading skill than any other faction. Also, it has the HMS Victory, which is awesome (although it won't make a big impact on your gameplay strategy). You can enter a naval battle knowing that ship-to-ship, you are superior. However that does not mean that you should act careless. After all, you are still outnumbered by the French, the Spanish, and the Pirates. The only factions that Great Britain might have trouble with, ship-to-ship, are France (extra hull strength on their ships) and America (extra reloading skill, 24-pounders being superior to Razees).
Great Britain has arguably the best line infantry in the game. They also get a couple of DLC line infantry such as the 33rd Foot and the King's Royal Regiment of New York, but honestly they aren't remarkable in terms of stats. One interesting thing to note is that their colonial line infantry aren't special and are far worse than their regular line infantry. If the time and money can be spared, it is better to train line infantry in Europe and then transport them to the Americas, instead. Colonial line infantry are always identical regardless of faction, it's just more noteworthy here because GB's default line infantry are so good and so much of the fighting will be in the Americas.
Great Britain has an above average guard roster with a couple of extra options, such as the Coldstream Guards and The Black Watch; these may only be trained in Scotland. Finally, Great Britain also has a few extra grenadiers, but they are unremarkable. Like Prussia, Great Britain already has excellent line infantry, so grenadiers aren't as beneficial in shoring up their weaknesses. Great Britain has probably the most interesting light infantry roster. Its green jackets are essentially reskinned riflemen, but Ferguson Riflemen are just insane: their fire rates are much higher than any other unit in the game, and they can quickly destroy nearly any regiment. Great Britain also has access to Fraser's Marksmen and Roger's Rangers--both excellent early-game skirmishers far better than almost any other option available to the other factions.
Great Britain's cavalry are unique as well. They don't have access to cuirassiers, and instead have heavy cavalry. They also get access to Tarleton's Light Dragoons, Life Guard (reskinned household cavalry but with extra morale) and Horse Guards, creating a formidable light and heavy cavalry roster.
Overall Great Britain's roster is pretty to look at with all its DLC options, but also one of the best in the game--particularly where infantry and cavalry are concerned.