Metro apps support multiple view states, namely:

• FullScreenLandscape
• Filled
• Snapped
• FullScreenPortrait [http://www.silverlightshow.net/items/Windows-8-Metro-Layout-view-states-and-navigation.aspx|See this article for more information on the states]

There are two ways to handle this, either you want to keep the same view model & just put an alternative view on it or you want an entirely new view & view model loaded.