<Canvas xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
 	xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">

  <TextBlock x:Name="text_one" Canvas.Left="10" Canvas.Top="10">
	line one
	<LineBreak />
	line two
	<LineBreak />
	line three
  </TextBlock>
  
  <TextBlock x:Name="text_two" Canvas.Left="10" Canvas.Top="100">Just one line</TextBlock>

</Canvas>

