<UserControl x:Class="WpfFrame.VisualShield ...>

	<UserControl.Resources>
		<local:YCoordinateConverter x:Key="YCoordinateConverter" />
	</UserControl.Resources>
	
		<Grid>
			….

			<Canvas Grid.Row="3"
					x:Name="canvas"
					Margin="0,4,0,0"
					Height="380"
					Width="40">
				
				<Line X1="20"
					  X2="20"
					  Y1="200"
					  Y2="{Binding Converter={StaticResource ZeroToYCoordinateConverter}, ConverterParameter=???}"
					  Stroke="Black"/>
					
				….

			</Canvas>

		</Grid>
	
</UserControl>

public partial class VisualShield : UserControl
	{
		public VisualShield(Model m)
		{
			InitializeComponent();

			this.DataContext = m;
		}
	}

	public class YCoordinateConverter : IValueConverter
	{
		public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
		{
                       // тут нужна модель переданная в  DataСontext
			….
		}

		public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
		{
			…..
		}
	}

<Line 
X1="20"
X2="20"
Y1="200"					  
 Stroke="Black">
  <Line.Y2>					
       <MultiBinding Converter="{StaticResource YCoordinateConverter}" >
              <Binding />
       </MultiBinding>
  </Line.Y2>
</Line>

public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
{
     // DataContext приходит в values[0], но Y2 не устанавливается
      return 300;
}

public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
{
      return (double)300.0;
}