Whether it is an escort aircraft carrier or an attack aircraft carrier, is not a question of tonnage.
Well, tonnage can certainly be one of the determining factors.
A "Jeep" or "Escort" carrier is going to be definitely a lot smaller than a "fleet carrier" CVN.
It will be designed to carry far less aircraft, and will be designed to provide protective cover for convoys and task forces...not to take an all out air campaign against an opponent on the land or at sea.
So where today a US Navy CVN is at 100,000 tons in order to accomplish the tasks outlined above. a US navy Escort carrier would be far less.
Some think that the new America class LHA could fit that "escort" role.
But the America class, while it can provide a decent air wing for what might be called the "escort" role, it is also built to do much more. It is designed to carry a couple of thousand Marines, and the helicopters to preform air assault with them. it is also built to provide close air support for them ashore. Those are not necessary for a true "escort" carrier.
So the 45,000 tons or so that an America class displaces is, IMHO, quite a bit larger than it would have to be to perform purely an escort duties.
If the US Navy builds an "scport carrier" class to augment the CVNs, it would probably be something about the size of the Cavour class...but with an angled deck and a couple of cats...with arrested landing on the stern.
I expect it would carry maybe a maximum of 24 aircraft, with 3 E-2Ds, a couple of CV-22s for COD, perhaps six ASW helos or aircraft, and then 12-14 F-35Cs.
if they wanted to make it a ski-jump type vessel, they could leave off the cats and use a ski-jump...but I do not think the US Navy would go that way.
It would have its own defenses...probably two Phalanx, two ESSMs and two RAM launchers, with several either 25mm or .50 cal guns. it would have decent air radar, sonar, and good comms and other sensors. it would be built to a good combat standard.
All in all I think such a vessel would be 800+ feet long, have a deck width of something less than 200 feet, and displace 30,000 tons or more.
But this is all getting well OT on the PLAN carrier thread so I will probably move the discussion about it to the Carriers Thread.