I'm thinking of buying this game from the e-shop when it comes out in Europe tomorrow, but I only have the 2GB SD card that comes with the 3DS. Does anyone know how big the download is for this game? I can't seem to find that info anywhere in the e-shop.

When you attempt to purchase something on the E-Shop it should show you the "blocks" required, as well as the blocks you currently have free. I can't get you the size since the game isn't available for download in NA. 
 
I will try to get the size off the Vita PSN when my vita finishes patching. 

@NyxFe: I'm definitely interested in hearing the Vita version's file size. It's probably indicative of the 3DS version.

PSN says 1.3GB so you should be fine, assuming there is no weird file buffering. The game is mostly audio files so I can't imagine the 3DS would change the size.

I downloaded it on to my 3DS and it's just over 3000 blocks if I remember correctly, I also have professor Layton and that was in the 4000's. I only have a 2gb memory card in my 3DS but thinking of getting a much larger one, does any one know how the data transfer from one SD card to another works only using one 3DS?

@Evan223 I've successfully moved data by simply copying it from one stick to another. I don't believe there's any trick to it, as long as the stick is formatted correctly (I think it's just FAT 32).