Unfortunately, wage labour plantations wouldn't be viable in anything remotely like the OTL antebellum South.
This isn't because wage labour couldn't be used to grow cotton or other crops. Paid labourers could grow cotton in the right circumstances (albeit at less of a profit than slaves). They could be used to grow most of the other OTL slave labour crops too - tobacco, rice, hemp, indigo, wheat. (Yes, wheat was a slave-grown crop). Maybe even sugar, although that would be more difficult (see below).
But while wage labour could be used to grow those crops, it would not lead to wage labour plantations.
This is because of the conditions of OTL North America. Land was very cheap, and labour was very expensive. Anyone could, and usually did, grab land if they wanted it. The problem was finding labour to work the land. If you paid a wage labourer to farm cotton, or anything else, within a handful of years, he'd be most likely to pack up and start his own farm.
The way the interior of North America was colonised shows this very well. Plantations did not, except in unusual circumstances, get set up in one go. What happened was that a few pioneers would move west, kill or otherwise push out the people who mistakenly thought that they owned the land, and then claim the land. Most of the time they didn't even pay the (American or Canadian) government for the land, or if they did, it was very cheap.
These pioneers would clear any vegetation, then set up new small farms (not plantations) on the best local land. The best local land would be the flattest, most fertile, and closest to transport (preferably a river, or sometimes railroads). Other people would follow, setting up more small farms pretty much wherever they wanted.
The problems came from how to work the farms. Where was the labour going to come from, when anyone who wanted to could grab their own land and be their own farmer?
The only people willing to work for these early farmers were usually their own families, plus some seasonal "hired help" from time to time. Usually this just meant people who didn't have much experience of farming - once they had worked out how to farm, they'd strike out on their own, either to nearby land or just pushing further west. Even to keep farmhands for a season or two was fairly expensive - and hired labourers were often known to go on strike for higher wages at crucial times (ie when the harvest needs to be brought in).
This meant that the size of most farms was quite limited to what a farmer could farm with the help of their immediate family and occasional help. Anything bigger than that, the only way to use the land was to sublet it to someone else. This didn't give much of a profit, since if you charged someone too much, they'd just strike out on their own. Land was just too cheap.
What happened next depended on whether slave labour was available. In the North, any successful small farmers couldn't really become large farmers. (Except by overeating). In the North, succesful farmers who grew wheat (or whatever) could invest in land speculation, but that wasn't all that profitable, for the reasons specified above. Or they could invest in grain mills - good, profitable idea - or into non-agricultural enterprises, which were mostly in burgeoning towns. This led to the growth of towns, and in time into manufacturing and industrialisation. This pattern might have changed for the North if slave labour was available (see below) or if different crops were available (Aururian crops, perhaps?), but not otherwise.
In the South, though, what could a successful farmer do? He (usually he) did not need to rely on hired help, since he could buy a slave. This got rid of the limit on farm size, since slaves couldn't strike out west and start their own farms. In the South, successful farmers could buy more and more slaves, take advantage of economies of scale, and in time buy out their neighbours and turn their lands into plantations.
From there, the profits would be reinvested into improving their plantations. Or, more precisely, on fancy clothes for themselves and their house slaves, throwing lavish parties, living it up, and then improving their plantations if there was any cash left over. But the profits were mostly kept into agricultural investment, which inhibited urban development, and was they there was relatively less industrialisation in the South. (Not none, though - far from it. But comparatively less than the North).
In other words, in North America plantations were a result of having slave labour. You couldn't build them otherwise, except in a few special circumstances, since land was so cheap and labour was very expensive.
Could this be changed? Perhaps, but not easily. The effects of cheap land and expensive labour are hard to muck about with, and resulted in some pretty deep-seated attitudes in North America. Their consequences were felt very early in the colonisation of North America, and would not be changed readily, and not without producing some other consequences.
For instance, in North America birth rates were much higher than in Europe, and population growth rates correspondingly rapid. This was because land was cheap in North America, making it easy for people to find and support a family, and because having a lot of kids on a farm was a good thing. (More workers, don'tchaknow.)
This also meant that the North American attitude toward working for wages was quite negative, and had been for a very long time. Native-born North American whites (Northerners, Southerners, and Canadians) wanted to be self-employed, not work for wages. Everyone in the country wanted to be a self-employed farmer, while everyone in the towns wanted to be a self-employed artisan or something like that, or better yet a wealthy landowner or industrialist.
Native-born North American whites - especially white men - were notoriously bad wage labourers in the nineteenth century. Ornery, obstinate, lazy, argumentative, inclined to go on strike, or show up for work late, drunk, nor not at all. Prone to quit at short or no notice, and generally do whatever they wanted. This affected both farmers and early urban industrialists. In Northern industry, it would eventually be solved by using under-employed white women and then by immigrants. In the South, they tried to get around it using slaves, but that didn't work so well when slave prices went up in the cotton boom, and slave labour was sucked out of early urban industries. But any entrepeneurial would-be wage-labourer plantation type would run into serious problems.
This also means that it's difficult to see any would-be entrepeneurial type even thinking of setting up a plantation with wage labour. Entrepeneurs in the South didn't usually think in those terms, since they didn't view land as particularly worthwhile.
For instance, Southerners were vehemently opposed to being taxed to pay for internal improvements. Internal improvements added to the value of the local land, but Southerners didn't care much about land values, whether rich or poor. Poor Southerners wanted to go somewhere else and try their hand at farming somewhere else. Wealthy Southerners were even more opposed, since most of their wealth was tied up in slaves. Slaves were mobile, but land wasn't - so being taxed on land was not attractive. If there was a need for internal improvements which would benefit a particular plantation or two, the planters would usually pay for it themselves - big plantations mostly had their own docks or railway stations, and warehouses - but they were vehemently opposed to being taxed to pay for someone else's internal improvements when it wouldn't do much for their own wealth.
In other words, any would-be entrepeneur who's working in wage labour is going to find that his wage labourers will go out and work somewhere else, and spending money on improving his own land won't really make it more productive, since he won't have any labour to work it. Better to buy slaves, since they can't quit, and that way if he does improve his own land, at least he's assured of having labour to work it.
Now, to change all this, you'd have to drastically change the nature of European settlement of North America. It could be done with big enough changes, sure [1] , but I doubt that this would be recognisable as anything resembling the antebellum South. If you confined European settlement to east of the Appalachians, then land prices would probably rise and population would grow, making labour cheaper, so maybe you could see wage labour plantations there, but that's nothing like the OTL South.
The other consideration is that slave labour also had some advantages over wage labour, particular in plantations.
One of the biggest advantages for slave labour - in some crops - is the gang system. This was a system where a gang of field workers would work as a team, on planting, harvesting, or whatever. They worked in a rhythm and at a pace which made them more productive per hour than other workers harvesting the same crops individually.
The problem is that free labourers hated working in a gang system. Absolutely loathed it, and flat out refused to do it in most cases. (Or demanded wages so high that it would have been unviable.) This meant that slave labourers harvesting in a gang system were more productive per hour) than hired labourers would have been (although not necessarily more productive per hour than a self-employed farmer).
This gave slave labour a considerable comparative advantage in certain crops. Gang labour was marvellous for cotton, and for sisal - although that didn't grow in the South). It was also, oddly enough, good for wheat, too. But it wasn't suitable for some other crops, such as rice, tobacco or sugar.
As an aside, slavery did work for sugar, though, but not for anything to do with the gang system. The main problem with sugar farming was that the death rates were atrocious - no sane free labourer (especially Europeans) wanted to work in farming sugar. Slaves could be forced to, but even then a lot of them died. That didn't matter to the sugar planters, since sugar was insanely profitable, and imported slaves were cheap. The general attitude was "plenty more slaves on the next ship".
Oddly enough, sugar farming conditions could have been improved if the planters had really wanted to. In the British West Indies, the slave trade was abolished in 1808 (or thereabouts), including the inter-island slave trade. Sugar planters now couldn't get more slaves. So they had to look after the ones that they had. Various improvements followed, and slave death rates were lowered, and the birth rates rose. (I can't remember if the overall slave population growth rate was positive or negative, though, but it definitely rose.) So maybe wage labour plantations could have worked with sugar, although it would have to be using black labourers, not white - the death rate for whites was still too high for them to be interested, I suspect.
As another aside, the fact that gang labour worked with wheat suggests that in the right (or rather, wrong) circumstances, slavery might have worked in the North, too. This would require that something had happened to stop the viability of cotton labour - Super Boll Weevil on steroids, perhaps - since the returns on cotton were so insanely profitable that slave labour was sucked into the cotton areas and out of other areas. But wheat (and other small grains, and hemp) could be and were grown profitably using slave labour in parts of the antebellum South - especially Virginia - so it could be done.
For instance, I think that a non-invention of the cotton gin was quite likely to strengthen slavery in the USA, not weaken it. In places like Indiana and Illinois, slaves were used in the early years, despite the Northwest Ordinance forbidding them there. Into the early 1820s, there were slaves being used to grow wheat, other small grains and hemp - Southerners brought them north from Kentucky and Virginia. This led to various calls for the legalisation of slavery in those states, including attempted constitutional conventions.
In OTL, these calls came to nothing, and slavery was never officially legalised in Indiana and Illinois. But this was because the cotton-gin inspired boom sucked most of the spare slave labour south into cotton plantations in Missisippi and Alabama. In an ATL without the cotton gin, you might not have many slaves growing cotton in Alabama (although you'd have more growing sugar along the coast), but you'd probably have a lot more slaves growing wheat in Illinois, Indiana and Kansas. Go figure.
Anyway, another big advantage of slavery was a high labour force participation rate. Most able-bodied slaves - men and women - worked in the fields (or in industries). Sure, free women weren't sitting around on their butts all day doing nothing, but their work didn't have the same direct economic benefits as slave women (say) growing cotton. Especially since in a plantation, child care would be organised on a group basis, with a few elderly or infirm slaves minding the small children. And the older children being dragooned into work, of course, such being the nature of slave life.
This is why when the slaves were freed in the South and mostly ended up sharecropping afterward, labour force participation rates plummeted. The former slave women still worked, but not in the cotton fields. Economic growth slowed considerably as a result.
Slave labour plantations may also have some advantages in economies of scale over wage labour plantations (if such things existed). Big plantations did have considerable advantage in economices of scale, since they were able to pay for their own internal internal improvements (see above), bulk purchases of food and clothes, etc. Maybe a wage labour plantation could imitate some of those improvements - providing its own cheap housing, perhaps - but not to the same overall effect, since free workers would be more inclined to demand better food and clothes, or at least higher wages to pay for the same.
Okay, that was much more long-winded than I'd originally planned, but the short version is that, unfortunately, wage labour plantations probably aren't viable in the South.
[1] For instance, in Lands of Red and Gold slave labour will be marginal in most of North America, as a result of a variety of butterflies. That might make wage labour more viable, if only because it reduces alternatives.