I am creating a height map to import into the dev kit to creat my landscape. My question is what should my canvas size be to successfully load it into the dev kit. My second question is should i do this in a 3d program or will the 2d one suffice?
Make your landscape first in the editor so you can get your size and resolution correct, then export the heightmap and load that into your editor. You can edit your heightmap in 2d or 3d if you want. For 3d I prefer worldmachine. I wouldn’t bother trying to use a sculpting program unless you are experienced with them, the built in landscape tools should be good enough.
But whats the size…
By size, I assume you mean the resolution your height map should be. If that’s the case, look on the left side of the ADK under the Landscape tab. You’ll see a section called ‘Overall Resolution’. That’s the resolution you need to make your height map.
Try my examples maps which are made at the max size 8129x8129: https://forums.unrealengine.com/showthread.php?120176-Duke-s-Free-Heightmaps&highlight=duke+free