Whatsapp will work only on a jailbroken iPad. That means if your iPad is not already jailbroken you need to do so.
1: Download and install the iPhone Configuration Utility from the links given below.
iPhone Configuration Utility for Windows
iPhone Configuration Utility for Mac
2: Connect your iPad with your Mac or PC.
3: Download WhatsApp for iPhone on your PC or Mac using iTunes.
4: Now launch the iPhone Configuration Utility. On the left hand side, you will see your connected iPad; click on it.
5: Click on Applications from the tabs you see at the top of your screen.
6: Click on Add at the top left and browse for the WhatsApp IPA file you download in Step 3. It can be found under the iTunes Media > Mobile Applications folder.
7: Scroll down and click on Install. WhatsApp will appear on your iPad’s Springboard.
8: On your iPad, open up Cydia and install WhatsPad tweak from the BigBoss repository.
Once the WhatsPad tweak has been installed, launch the WhatsApp app from your homescreen and it will work the way it works on your iPhone. WhatsApp will ask you to enter a PIN for activation which you’ll receive in a text message, therefore be sure to activate WhatsApp using your active phone number on which you can receive text messages in order to get the PIN. Enjoy whatsapp