var scaleTrans = new ScaleTransform();
var xBinding = new Binding("Value") { ElementName = "zoom" };
var yBinding = new Binding("Value") { ElementName = "zoom" };

BindingOperations.SetBinding(scaleTrans, ScaleTransform.ScaleXProperty, xBinding);
BindingOperations.SetBinding(scaleTrans, ScaleTransform.ScaleYProperty, yBinding);

var canvas = new Canvas
{
    Background = Brushes.White,
    Margin = new Thickness(0,10,0,10),
    Effect = new DropShadowEffect
    {
        Color = Colors.Gray,
        Opacity = 0.5,
        ShadowDepth = 3
    },
    LayoutTransform = scaleTrans
};

SetCanvasSize(PageOrientation, canvas);
mainGrid.RowDefinitions.Add(new RowDefinition { Height = GridLength.Auto });
mainGrid.Children.Add(canvas);
Grid.SetRow(canvas, mainGrid.RowDefinitions.Count - 1);

class Paginator : DocumentPaginator
{
    private readonly List<Canvas> pageList = new List<Canvas>();

    public void AddPage(Canvas canvas)
    {
        pageList.Add(canvas);
    }

    public override DocumentPage GetPage(int pageNumber)
    {       
        return new DocumentPage(pageList[pageNumber]);
    }

    public override bool IsPageCountValid
    {
        get { return true; }
    }

    public override int PageCount
    {
        get { return pageList.Count; }
    }

    public override Size PageSize
    {
        get
        {
            return new Size(pageList.FirstOrDefault().Width, pageList.FirstOrDefault().Height);
        }
        set
        {
            throw new NotImplementedException();
        }
    }

    public override IDocumentPaginatorSource Source
    {
        get { return null; }
    }
}

var printDialog = new PrintDialog();
if (printDialog.ShowDialog() == true)
{
    var paginator = new Paginator();
    foreach (UIElement item in mainGrid.Children)
    {
        var canvas = item as Canvas;
        if (canvas == null) continue;
        paginator.AddPage(canvas);
    }
    printDialog.PrintDocument(paginator, "Demo Print");
}