Making The Game Fullscreen

There are several options for making your game fullscreen.
Hardware fullscreen is an option. It's probably not the best option, however.
Borderless fullscreen is the modern option. Let's discuss them both.
Note: these code examples refer to Game1.Initialize().

Option 1 - Borderless Fullscreen

protected override void Initialize()
{
	base.Initialize();

	int displayWidth = GraphicsAdapter.DefaultAdapter.CurrentDisplayMode.Width;
	int displayHeight = GraphicsAdapter.DefaultAdapter.CurrentDisplayMode.Height;
	graphics.PreferredBackBufferWidth = displayWidth;
	graphics.PreferredBackBufferHeight = displayHeight;

	this.IsMouseVisible = true;
	Window.IsBorderless = true;
	graphics.ApplyChanges();
}

Pros

The game starts fullscreen, without any border or title bar.
The best option. You should provide a way to exit the game.

Cons

Option 2 - Hardware Fullscreen

protected override void Initialize()
{
	base.Initialize();
	graphics.ToggleFullScreen();
	graphics.ApplyChanges();
}

Pros

Your game will be stretched to match the user's screen resolution.
No additional code is necessary to ensure your game displays fullscreen.

Cons

If the ratio of your game window doesn't match the user's display ratio, your game will appear distorted.
You don't have control over how your game will be displayed across different resolutions.
Alt-Tabbing to different programs may cause problems.
Textures and Fonts will be stretched as well, usually with blurry results.
By default the game window's titlebar will be hidden.