Sync to ancestors properties

<Canvas>

  <DockPanel

      Width="{Binding RelativeSource=

                {RelativeSource FindAncestor,

                AncestorType={x:Type Canvas}},

                Path=ActualWidth}"

      Height="{Binding RelativeSource=

                {RelativeSource FindAncestor,

                AncestorType={x:Type Canvas}},

                Path=ActualHeight}">

  </DockPanel>

</Canvas>