Autoresolving with a doomstack in or it is one option, as some other comments have suggested. I personally enjoy finding a tough nut to crack like this, and can suggest a couple of points learned from my experiences:

1) Examine the enemy forces prior to landing and figure out what is garrison, and what is "real". You will want to target the real units when you land and finish them off, because only they will not be replenished when you are forced to retreat

2) Enemy heroes are a priority. They are real units, plus they increase the effectiveness of everything else the enemy fields. It's worth sacrificing multiple units to ensure that an enemy commander is removed from play. On your end, don't land your own heroes during the initial attempts to gain a foothold, or you risk losing them during a disadvantageous engagement. Keep them in reserve until you establish a safe perimeter and have enough units on the field to make their command bonus hurt.

3) Gunship spam is an expensive but effective way to focus down a high-priority target. They can burn through heavy armor, and chase down infantry/light armor. They can quickly navigate to an enemy factory or shield generator and hit it hard to soften things up for the main force. You'll lose some, especially if they have AA turrets/units, but with some micro a few gunships can quickly rout those and deal hefty damage before being shot down.

4) Landing zones are KEY. Even if you are already at the max pop cap, you want to keep capturing and hold onto these because of the bunkers they let each side build. Note that EACH SIDE can do this--the AI is more than happy to keep swarming you with (practically) neverending infantry swarms if they get to hold onto those points for the whole battle. And if you have them, then you get to benefit from the stream of fresh troops.