uGUI change depending on screen aspect ratio

Using the new uGUI, what's the best way to vary something in the GUI (say, whether there are one or two columns in a list, or whether a button is an icon, text, or icon+text) based on the screen aspect ratio (e.g. landscape or portrait).

The challenge is that in landscape you want to use the wider screen (say have more columns of data, or add text to icon buttons), but in portrait you don't have that space (say one column of data, or only room for an icon on a button).

In addition to having the correct layout at launch, it has to update the GUI if a mobile device is rotated to a new orientation.

What's the best way to set this up?