Good question. Be aware, though, that slavery existed throughout the British North American colonies, and covers a time span of at least 200 years from settlement to the US Civil War. The traditional "North vs South" division of free-vs-slave states didn't arise until the first half of the 19th century, and even then was somewhat nuanced. I also know that - at least initially - Native Americans were enslaved and used as laborers.

1493, by Charles Mann, indicated that some Native Americans were enslaved (within the context of his discussion on Jamestown and what followed there), but that they made poor slaves because they knew how to escape and could take advantage of their superior knowledge of the environment to survive until (I presume) they returned to their tribes.

African slaves would not possess such knowledge.

Piggybacking off this: I've read about Irish slaves in Barbados and South Carolina. Could somebody tell me how true that is?

Each state would have their own Slave Codes defining who can be enslaved. In general whites were not considered slaves even if they were held in indentured servitude. Some examples:

Virginia, 1705: "All servants imported and brought into the Country...who were not Christians in their native Country...shall be accounted and be slaves. All Negro, mulatto and Indian slaves within this dominion...shall be held to be real estate."

.

South Carolina, 1712: "Be it therefore enacted, by his Excellency, William, Lord Craven, Palatine.... and the rest of the members of the General Assembly, now met at Charles Town, for the South-west part of this Province, and by the authority of the same, That all negroes, mulattoes, mestizo's or Indians, which at any time heretofore have been sold, or now are held or taken to be, or hereafter shall be bought and sold for slaves, are hereby declared slaves; and they, and their children, are hereby made and declared slaves..."

Conversely, were there any black slave owners?

I've heard about the Irish being slaves. Was that a thing?

Followup question: Was there any legal requirement that slaves be of certain origin? Or just they had to be imported as slaves? Could a trader have theoretically rounded up some Germans or English and imported them as slaves?

A buddy of mine went down to south Louisiana, and took a tour of some old slave lands/houses. There were portraits on the walls of some black men, women, and children. He said, "That's nice of the slaveowners to have pictures up of their slaves." Thinking totally innocent thoughts. When the tour guide said, "Oh no, those aren't the slaves. Those are the owners!"

Hah! I don't know the race of the slaves they had, but just the fact that blacks owned slaves was a huge surprise to me!!

I am certainly no expert, but a while ago I read a book about Salome Muller and the funk surrounding her in Louisiana (New Orleans, I think) and how she may or may not have been white or mulatto, and it is hard to believe that she was the only (possible) indentured servant child brought up believing they were of African descent somewhere along the line due to their condition of slavery. Just a thought, and a half baked one at that, though ;)