Use the four attached properties of the Canvas element: Bottom, Left, Right, and Top
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<Page xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
WindowTitle="Canvas Attached Properties Sample">
<Border HorizontalAlignment="Left" VerticalAlignment="Top" BorderBrush="Black" BorderThickness="2">
<Canvas Background="LightBlue" Width="400" Height="400">
<Button Canvas.Top="50">Canvas.Top="50"</Button>
<Button Canvas.Bottom="50">Canvas.Bottom="50"</Button>
<Button Canvas.Left="50">Canvas.Left="50"</Button>
<Button Canvas.Right="50">Canvas.Right="50"</Button>
</Canvas>
</Border>
</Page>
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