you can create a prefab from all of the assets in your map and export it to a .xml in ce2 then load that up into your heightmap in ce3.
Note: you need the appropriate textures and models in their places in the Crysis 2 folder.
To create the prefab select all of your objects:
1. Ctrl + T then click select all.
2. in the toolbar click prefab >Create from selection
3. the database view window will pop up, name the prefab - do not fill in the "group" box
4. right click on your prefab and select copy or cut
5. select any existing prefab library, you may have to load one (to paste you must right click on an existing prefab in the loaded library)
6. click the save changes button in database view
7. go to you crysis wars/game/ and copy your prefabs folder to the crysis 2\gamecrysis2\ folder ( Note: rename your prefab.xml file in the prefabs folder to something memorable, such as the map name)
8. fire up CE3, load your level, go to database view>prefabs tab>load library > select your custom library