I'm inclined to think both Imperial Soldiers and Guard are British as well. In my current MOC I've got blue sailors all over the ship-of-the-line that's docked, and the redcoats are stationed at the port. Not that a regiment of redcoat marines would be out of place on a ship, but this isn't exactly a large warship.
Granted the French had several uniforms that looked really similar to the stock blue/white with bandoliers, but generally speaking the uniforms seem obviously British. Red for marines, blue for sailors.
Interestingly enough, grenadiers from Nassau wore a variant of the basic Soldier torso, in green. So if you want Jamaican soldiers, Lego has green arms, and the Soldiers torso pattern can't be too hard to find.
There's a lot more leeway with the decorative "admiral" torsos - I've seen identical jackets on uniforms from British, French, Croatian, Maltese, and a dozen other naval officers in the Napoleonic era.
An 1815 French officer could actually be made with parts already existing if Lego felt like making a French faction. Black torso (maybe the classic Fireman torso) with the chrome "Conquistador" armor over it. Black sleeves. White gloves. Yellow epilets. Tan pants. And a chrome Dragon Master helmet with a red feather.
An 1815 French grenadier could also be made - the blue/white torso, red epilets, white pants, tall hat. I'd keep the blue sleeves and actually give him red gloves to add the necessary red element.
Lastly, a French lancer could be made too. Red pants, red sleeves, tan hands, yellow epilets, and a Paradisa red dinner jacket (although I'd rather see it done accurately with the black collar and trimming, and white bandolier over it).
But anyway ... yeah ... British.