Instead of putting (as in your example) a button directly on the canvas, you could put a stackpanel on the canvas, horizontally aligned, and put the two buttons in there.
Like so:
<Canvas>
<StackPanel Canvas.Left="100" Canvas.Top="100" Orientation="Horizontal">
<Button>Button 1</Button><Button>Button 2</Button>
</StackPanel>
</Canvas>
I think that it’s quite flexible when you use more than 1 layout in a form, and you can create pretty much any configuration you want.