Just thought i'd share this with anyone who needs more clarity on how to achieve this:
myCanvas is a Canvas control and Parent to all other controllers. This code works to neatly resize to any resolution from 1366 x 768 upward. Tested up to 4k resolution 4096 x 2160
Take note of all the MainWindow property settings (WindowStartupLocation, SizeToContent and WindowState) - important for this to work correctly - WindowState for my user case requirement was Maximized
xaml
<Window x:Name="mainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:MyApp"
xmlns:ed="http://schemas.microsoft.com/expression/2010/drawing"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008" xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" mc:Ignorable="d"
x:Class="MyApp.MainWindow"
Title="MainWindow" SizeChanged="MainWindow_SizeChanged"
Width="1366" Height="768" WindowState="Maximized" WindowStartupLocation="CenterOwner" SizeToContent="WidthAndHeight">
<Canvas x:Name="myCanvas" HorizontalAlignment="Left" Height="768" VerticalAlignment="Top" Width="1356">
<Image x:Name="maxresdefault_1_1__jpg" Source="maxresdefault-1[1].jpg" Stretch="Fill" Opacity="0.6" Height="767" Canvas.Left="-6" Width="1366"/>
<Separator Margin="0" Background="#FF302D2D" Foreground="#FF111010" Height="0" Canvas.Left="-811" Canvas.Top="148" Width="766"/>
<Separator Margin="0" Background="#FF302D2D" Foreground="#FF111010" HorizontalAlignment="Right" Width="210" Height="0" Canvas.Left="1653" Canvas.Top="102"/>
<Image x:Name="imgscroll" Source="BcaKKb47i[1].png" Stretch="Fill" RenderTransformOrigin="0.5,0.5" Height="523" Canvas.Left="-3" Canvas.Top="122" Width="580">
<Image.RenderTransform>
<TransformGroup>
<ScaleTransform/>
<SkewTransform/>
<RotateTransform Angle="89.093"/>
<TranslateTransform/>
</TransformGroup>
</Image.RenderTransform>
</Image>
.cs
private void MainWindow_SizeChanged(object sender, SizeChangedEventArgs e)
{
myCanvas.Width = e.NewSize.Width;
myCanvas.Height = e.NewSize.Height;
double xChange = 1, yChange = 1;
if (e.PreviousSize.Width != 0)
xChange = (e.NewSize.Width / e.PreviousSize.Width);
if (e.PreviousSize.Height != 0)
yChange = (e.NewSize.Height / e.PreviousSize.Height);
ScaleTransform scale = new ScaleTransform(myCanvas.LayoutTransform.Value.M11 * xChange, myCanvas.LayoutTransform.Value.M22 * yChange);
myCanvas.LayoutTransform = scale;
myCanvas.UpdateLayout();
}