I was doing some more thinking about the DSA's Demographics in 1850.
Essentially it can be divided into three. The Caribbean (including Puerto Rico) was 70% Black in OTL and has a population around 700,000.
Indeed.
The West is essentially empty as far as settled people who acknowledge the authority of the DSA are concerned.
In other words, filled with 'wild' Indians.
That leaves the "South" or really the East, as as far as the DSA is concerned the Caribbean islands are its South. In 1850 in *OTL the population of the entire South was around 8 million with around 3.2 million slaves and an estimated 250,000 Indians. That means a total for the *DSA in OTL of 9 million adding in 300,000 American Indians in the West.
So some more Indians and Blacks than OTL.
Now we can assume that the Caribbean is essentially the same with Puerto Rico added
Well, there's been some significant immigration to Richport (OTL Puerto Rico) of Loyalists and other British. Not a majority, but they're a power in the land as it were.
and that the Black population in the East is roughly similar to OTL.
Slightly higher at the time of the Slaver Uprising - then between 1840 and 1865 it will grow less than OTL did in the same period. After that probably will grow slightly less than OTL as well, but not as dramatic of a difference.
However the big question is White immigration and Indian survival. Sad as it is the American Indian population was falling as famine and war destroyed the tribes. Here that is not true, or at least not as true. This is obviously going to have an effect. The other addition is the "East" Indian immigration. While Glen hasn't given details I doubt it would be more than 200,000 or so, if only due to cost and most would be heading for the empty West rather than the fuller East.
The Civilized Tribe population will definitely be higher without the Trail of Tears. The 'East Indian' Population will grow in the West, but you are wrong about the East not having substantial numbers come there as they are in fact being brought in to plantations to work, as well as in the Caribbean.
Now lets say that additional immigration pushes the White population from 4.7 million in OTL to 5.5 million (17% more) and less genocide means the American Indian population stays static at 600,000 between 1830 and 1850 rather than dropping as growth among the Civilised tribes cancels out deaths among the uncivilised. Add in 250,000 East Indians (natural increase) and 3.65 million Blacks we have a total of 10 million for the DSA in 1850. All these figures are just my guesses, its your sandbox.
Probably go a bit higher with the East Indians (though maybe not - it is still early days) and higher with the Blacks a bit.
This means there are going to be major regional differences with a Majority Black Caribbean, narrow white majority South-East, a North East (i.e. the border provinces that Glen mentioned) that is in order American Indian/White/Black and a White/American Indian/East Indian/Black West. This is because I guess that the majority of settlers will be White either straight from Europe or from the East adding to the local Indians and "East" Indians brought in for the railways, Black migration West will be held down by poverty and discrimination. This regional difference is obviously going to bring a lot of diversity but also political tension with more regional identification than in the more homogeneous USA.
True there will be different distributions, though you underestimate black immigration to the West, which will in fact be substantial as poverty will drive more west than keep them east, and the flavor of discrimination in the DSA will actually tend to 'encourage' ungainfully employed blacks to leave the civilized provinces, and the territories the closest place for someone to go to (besides America, of course, but they will do some counter-persuading of anyone who doesn't find work fast). So blacks of the east will migrate towards west and secondarily northwest. It won't be a tidal wave, but a steady tributary of the streams of settlers heading West.
On another issue you mentioned that all who fought for the Loyalists have been given the vote and their children. Can you explain why? In Britain at this time the vote wasn't given to veterans and the vote wasn't hereditary, you could be kicked off the electoral roll if you lost you money. So why this very unusual provision?
The Loyalists and British wanted to ensure that the government of the DSA would stay staunchly loyal to the British Empire, and so they made certain that Loyalists and their families could not be disenfranchised (including blacks in this case, which was actually a compromise, by promising that Loyalist blacks would be 'special' cases with regard to suffrage, it made the laws that would disenfranchise so many others of the blacks of the DSA more 'palatable' to the Loyalist whites who felt a loyalty to their dark-skinned comrades in arms). I did hesitate on making it hereditary, but in the end I think they went this extra step in the DSA - the family of a man who fought for the Empire can only be disenfranchised should he, or one of his descendants, take up arms against the British Empire.