Well, an extreme POD, but avoid the Cold War, don't have any sort of anti-Communist backlash, maybe society in general's views will be more left wing...
I think this is the right way to do it. Without the Civil War you would still have the massive industrialization seen post-Civil War iOTL, but without the unifying experience of the Civil War to keep labor violence out of the equation. You would also have a different kind of army, because Captains of Industry would not be staffing their corporations (which would also look far different- maybe not even exist- without the 14th amendment) with generals.
Basically, I think that without the Civil War, you would still see things like the Pullman Strike, but with the country on an entirely different legal/constitutional footing, there is much more chance for violence. The government would probably be far less willing to call out federal forces (since strong states' rights positions were never undermined by the Civil War) to put down strikes, and the state militias that would be called out would probably be pretty sympathetic to the plight of their fellow working man.
Also consider the lengths to which anti-slavery activists went to reach their aims, going so far as to support things like "bloody Kansas" and John Brown's Rebellion. Once "industrial servitude" starts in the North, on the truly massive scale witnessed post-Civil War OTL I think you'll see that radical attention (which was never disapated by the Civil War) turned to causes closer to home.
So the political calculus would be different, the legal/constitutional environment MUCH different (both arguably improved by the Civil War to the point where they could deal with labor unrest- and conversely not improved in this TL) but the industrialization happens anyway.
I think this is a recipe for labor unrest. I think that its quite possible that the ethnic city machines end up trending much more left, with urban radicals being supported by urban machines. On the other side, the factory owner and the plantation owner find they have much in common, mainly keeping down unruly workers (eventual government-backed manumission would probably create some kind of alt-share cropper system- more legal, and more unfair) and making sure that the government doesn't regulate anything they don't want it to. Neither wants the Homestead Act, since that might relieve pressure in the cities and drive up labor costs, both want railroads to deliver goods across the country. The Solid South becomes solidly Cotton Whig (factory owners and plantations owners) as many former northern reformers decide that law and order (or just plain anti-organized labor) trumps any discomfort over the way blacks are treated. Urban radicals, an authoritarian-faux-aristocratic ownership class, yes sir, it has the makings for a serious Socialist Party.