<ToggleButton Height="100" Width="200" IsChecked="False" Checked="ToggleButton_Checked" Unchecked="ToggleButton_Unchecked" ></ToggleButton>
Hi just set the visibility of the grid visible and Collapsed(by default set Collapsed)
<Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}" Visibility="Collapsed">
when you checked the toggle button set your g1 grid visibility to visible and g2 hide it vice versa