User blog comment:Plexioth- xD/Monster Hunter 3 Ultimate/@comment-4452412-20130211135259

Yuri has confirmed that the 3DS demo will be single player only :(

Source:http://www.capcom-unity.com/ask_capcom/go/thread/view/7371/29766523/mh3u-demo-has-local-wireless-play-for-3ds-right&pg=last&528932949