Can entite project /landscape and archictecture be exported to eu4 (project in progress)
No really.
You need to import all your raw assets (fbx, etc.) in UE4 and setup eyerything again.
Depending how far your project is and your specific project, you might want to finish it in UDK and start the next one in UE4.
Beside all the raw assets you can also export BSP brushes with such tools: https://forums.unrealengine/showthread.php?4907-Tool-UE4-T3D-Converter-for-bsp-brushes 
The landscape can be exported and imported as a heightmap (raw16) -> gizmo tool