Probably both. Didn't he commanded both of those corps as one before his death? The Lee split it into two? Lee's plan to split his army into three corps was begun long before Chancellorsville and would have happened regardless of whether Jackson had been killed or not. He had felt for some time that two corps of four divisions each was unwieldy. Lee would have started his campaign under the new organization and Ewell would have commanded the third corps.
"Ewell would have commanded the third corps"
Why do you say this? I have not read that before. Hill had acquitted himself quite well to that point except for not being able to get along with his superiors. He fought hardest in the 7 days and was the hero who saved the day at Antietam. Ewell was a good fighter with a good rep but had been pretty much out of commission since losing his leg at 2 Manasses and was, as such, a bit of an unknown quantity.
We have no way of knowing if Jackson would have arrived at Gettysburg Henry Kyd Douglas was a staff officer for Gen Jackson, who kept a concise journal, over his campaign. A nephew published it well after the war - it is used today as THE accurate source of much of the Shenadoah campaign.
In fact it was used (by actor Steven Lang) who did a great job here; in a very historical-factual 'goodbye' when Jackson was promoted upstairs from the VA First Brigade General. There was, more he said, but this condensed version was quite accurate, and almost exactly from Henry Kyd Douglas' notes.
If I screw it up - someone pls fix the HTML;
https://www.youtube.com/watch?v=29HFaG9aOqo
