The console doesn't matter. You can transfer from 3DS A to 3DS B using a Wii U, and you can transfer from Wii U A to Wii U B using a 3DS. Just make sure to launch the game at least once (until main menu) if you never launched it on a console so that it creates Extended data slot, otherwise you won't be able to transfer Extended data (guild cards etc.).
Ping's MH3G Dex: A comprehensive, convenient and accurate MH3U database for Windows/Android/iOS. https://sites.google.com/site/pingsmh3gdex/