Use a Thumb to resize a Canvas control by responding to the DragDelta event.

   
  

<Canvas xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    x:Class="Thumb_wcp.Pane1">
  <Canvas Width="100" Height="100" Name="myCanvasStretch">
    <TextBox Name="changes" 
         Width="{Binding ElementName=myCanvasStretch,Path=Width}"  
         Height="{Binding ElementName=myCanvasStretch,Path=Height}" 
         Text="Size: 100, 100"/>
    <Thumb Name="myThumb" Canvas.Left="80" Canvas.Top="80" Background="Blue" 
          Width="20" Height="20" DragDelta="onDragDelta"/>
  </Canvas>
</Canvas>
//File:Window.xaml.cs


using System;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Controls.Primitives;
using System.Windows.Documents;
using System.Windows.Navigation;
using System.Windows.Shapes;
using System.Windows.Data;
using System.Windows.Media;

namespace Thumb_wcp
{
    public partial class Pane1 : Canvas
    {
        void onDragDelta(object sender, DragDeltaEventArgs e)
        {
            double yadjust = myCanvasStretch.Height + e.VerticalChange;
            double xadjust = myCanvasStretch.Width + e.HorizontalChange;
            if ((xadjust >= 0) &amp;&amp; (yadjust >= 0))
            {
                myCanvasStretch.Width = xadjust;
                myCanvasStretch.Height = yadjust;
                Canvas.SetLeft(myThumb, Canvas.GetLeft(myThumb) + e.HorizontalChange);
                Canvas.SetTop(myThumb, Canvas.GetTop(myThumb) + e.VerticalChange);
                Console.WriteLine(myCanvasStretch.Width);
                Console.WriteLine(myCanvasStretch.Height);
            }
        }

    }
}