Sorry for the delay and the longest headline ever but the eagerly awaited tools are available. According to my handlers:

We can now confirm that both MONSTER HUNTER’ 3 Ultimate Data Transfer Program (3DS download) and MONSTER HUNTER 3 ULTIMATE Packet Relay Tools (Wii U download) are available on respective eShops!

To help you locate the programs, type ‘Monster Hunter’ on the search bar in each platform’s respective eShop and you should be able to see Kayamba’s icon for 3DS and Felyne for Wii U”

Here’s what they look like.

Here’s is the 3DS Data Transfer Program icon
Here is the Wii U Packet Relay Tools icon

and now for the official statements related to these tools:

Fans who own both consoles, as well as a copy of the game for each system, can use the Monster Hunter’ 3 Ultimate Data Transfer Program to transfer their progress from one console to the other and vice versa for a seamless experience between hunting on the go and in front of the TV. This application will be available on Nintendo eShop on Nintendo 3DS.

 The Monster Hunter 3 Ultimate Packet Relay Tool for Nintendo 3DS is an application that can be downloaded for free from the Nintendo eShop on Wii U in order to play the title online on your Nintendo 3DS, via a Wii U console connected to the internet.

This application allows players of Monster Hunter 3 Ultimate on Nintendo 3DS to play the game online by using a Wii U console connected to the Internet via the Wii LAN Adapter or Wii U LAN Adapter (to be sold separately). Using this set-up, one Nintendo 3DS system can connect to the Wii U console, and play Monster Hunter 3 Ultimate online with other players, provided the online game is hosted by another player playing the game on Wii U. Please note that while the Wii U console is providing this function for the Nintendo 3DS system, it is not possible to simultaneously use the Wii U console for playing Wii U software or to connect locally to another Nintendo 3DS system. A copy of Monster Hunter 3 Ultimate for Wii U is not required.