There are a few Old Expanded Universe canonical options you could try to give the Rebel AI more of a fighting chance.

Victory Class Star Destroyers outnumbered Imperial Class Star Destroyers by a large margin. Only build 1 Imp-Star for every 4 Vic-Stars you build.

A lot of the Empire's search for Rebel Bases in the Outer Rim was conducted by Dreadnaughts. Build and use Dreadnaughts to hunt for the Rebels in the Outer Rim instead of Probe Droids or other faster vessels.

If you use the above options, you will need to rely on Escort Carriers to provide fighter support, which will slow down building your navy and put you at a greater disadvantage against Rebel fighters.

Although TIE Interceptors were 100% superior to TIE Fighters, the Empire continued building TIE Fighters in large numbers. The Empire's TIE Ratio aboard an Imp-Star was, 3 TIE Fighters, 2 TIE Bombers, 1 TIE Interceptor.
If you maintain this ratio in your game, you give the Rebel fighters an advantage because their fighters are superior to TIE Fighters.

Canonically, Lancer Frigates cost the same as an Imp-Star due to the large amount of experimental technology onboard. Maintain a 1 to 1 build of Imp-Stars to Lancer Frigates.

Despite the value of the Interdictor Cruisers, they were expensive to build, so only a small number were ever built. Do the same, and only build 1 for your main fleet, 1 for Coruscant, and 1 extra to cover damage and loses as the AI likes to focus fire Interdictors even when they have superior naval force.

The Empire relied heavily on Carrack Cruisers and Strike Cruisers to fill the gaps in their fleets, both of which greatly outnumbered both Vic-Stars and Imp-Stars. Build 2-4 of those ships, for every Vic-Star and Imp-Star you build.
Grand Admiral Thrawn's fleet had 5 Imp-Stars, 12 Strike Cruisers, 24 Carrack Cruisers, 1 Escort Carrier, and all ships only carried TIE Fighters.

Defend every planet you control. The Empire always had to appear to be defending every planet. If you spend time putting troops and fleets on every planet, you will have far less to throw at the Rebels while giving them more time to prepare.

Despite popular belief, Stormtroopers only made up a very small percentage of the Army, only 1% of the troops (not counting crew) onboard the Death Star were Stormtroopers. Build Army and Navy Regiments instead of Stormtroopers most of the time.

Don't build Darktroopers. By the time you research Darktroopers, canonically Kyle Katarn destroyed the Arc Hammer where Darktroopers were designed and built.

Canonically, the Empire spent more time using Diplomacy to subvert planets it didn't invade. Rely on Diplomacy instead of Incite Uprising.

Instead of using your high Leadership Characters to Incite Uprisings, do what the Empire did and put them in charge of Fleets, Armies, and Fighter Squadrons, Admirals, Generals, Commanders respectively. When you commit your leaders to actually leading instead of subverting control, the Rebels have more time to prepare a fight.

Blockade planets instead of Inciting Uprisings. This not only reduces your available ships, but is also the canonical way the Empire denied resources to the Rebels.

Best thing to do is do not attack your opponent's economy, makes the game too easy if you attack it. Leave Mines, Refineries, and Production buildings intact. This will give them more to throw at you. I always had a much harder time when I left the AI's economy and production intact.


As for Rebel Handicaps; canonical.

The Rebels used both Diplomacy and Incite Uprisings in equal measure, canonically. For a challenge, only rely on Incite Uprising in the Core Worlds, meaning you have to steal planets away from the Empire instead of converting neutrals.

The Rebels had very limited starship manufacturing canonically, all of it centered on Mon Calamari. They could only manage to build 2 Mon Cal Cruisers and 12 other capital vessels per year. Maintain that ratio as the Rebels.

Canonically, Y-Wings were almost as abundant as TIE Fighters in the galaxy. Build 2-3 Y-Wings for 1 of anything else.

Don't build any of the made up ships that were created for the game to balance out the Rebels, Dauntless Cruisers, Liberator Cruisers, CC-7700 Interdictors, Bulwark Battle Cruisers, CC-9600 Cruisers.
Only build Dreadnaughts, Escort Carriers, Mon Cal Cruisers, Corvettes, Gunships, Bulk Cruisers, Medium Transports, Bulk Freighters, Nebulon-B Frigates, Assault Frigates.

If you want to limit your ability to use troops to invade planets, don't build Bulk Freighters.

Invest all of your expansion effort in the Outer Rim, which is what the Rebels did canonically. Don't spend any time or resources on the Core Worlds. This will greatly slow you down as you have to build up from scratch, and give the Empire free reign of the Core Worlds.

Despite the value of B-Wings, the Rebels didn't have a lot of them. A typical Mon Cal carried 1 X-Wing, 1 Y-Wing, and 1 A-Wing into battle.

Consider relying on A-Wings instead of X-Wings. A-Wings lack the firepower to be a threat to capital ships, although they will kill TIEs faster then X-Wings.

If you want to be canonical, don't build Mon Cal Regiments if you don't control Mon Calamari, Wookiee Regiments without Kashyyk, or Sullustan Regiments without Sullust.

Again, best thing you can do is to leave the AI's economy and production intact.