I do not believe there were any Confederate Generals who were anti-slavery. In 1861 it was actually quite dangerous for any American citizen to express anti-slavery views while in the South. You will see quotes from men such as Lee which indicate slavery is an evil but Lee is also recorded as voicing the predominant opinion that it was an evil which God inflicts on black people and God will decide to end in his own time.

The Union side was much more complex of a story. The Democratic Party and the large number of voting public had a long history of agreeing with Southern slave owners. Most enlisted for the Union. Not to end slavery. But very many of those voted Republican in the 1864 election which was clearly anti-slavery.

Roughly two hundred thousand Southerners joined the Union army. Mostly coming from the border states but coming from all of them except SC. as a sweeping statement, they were more motivated in loyalty to their country than to slavery and their state. Many northerners joined the war, many were force conscripted and they joined with no interest to fight and die with the goal of ending slavery.

There were Republicans and Abolitionists who were the first to join the Union army with the singular goal of ending slavery. The Commander in chief, Lincoln, navigated the slow and steady path of enlisting border states and Union men into the cause. It took time and a lot of blood before the objective of the war changed. The Emancipation proclamation changed it from the preservation of the union to the extinction of slavery and thus permanently end the agitation. Public opinion of Northerns changed greatly with time to the point they ended up arming black men and paying them equally in the army. So, not only did a lot of men vary but they varied in time as well.

I will call out the top Union General of them all as pro-slavery. General McClellan. But I won't critique him. I will let Frederick Douglas do that.

Frederick Douglas wrote "McClellan, in command of the army, had been trying, apparently, to put down the rebellion without hurting the rebels, certainly without hurting slavery, and the government had seemed to cooperate with him in both respects. "

"I, however, faithfully believed, and loudly proclaimed my belief, that the rebellion would be suppressed, the Union preserved, the slaves emancipated and that the colored soldiers would in the end have justice done them. This confidence was immeasurably strengthened when I saw Gen. George B. McClellan relieved from the command of the army of the Potomac and Gen. U. S. Grant"

"With this condition of national affairs came the summer of 1864, and with it the revived Democratic party with the story in its mouth that the war was a failure, and with it Gen. George B. McClellan, the greatest failure of the war, as its candidate for the presidency. It is needless to say that the success of such a party, on such a platform, with such a candidate, at such a time, would have been a fatal calamity. All that had been done toward suppressing the rebellion and abolishing slavery would have proved of no avail, and the final settlement between the two sections of the Republic touching slavery and the right of secession would have been left to tear and rend the country again at no distant future."