How do you create a UI that is always landscape?

I am making a plugin for Unity that must support portrait or landscape games, but I want one of my ingame screens to always display in landscape, no matter the device orientation.

If the end user has a portrait only game, how can I make one of my canvases display in landscape, so the user has to rotate their device to the side to be able to interact with it? Creating a scaling UI that looks correct in portrait is not suitable for my needs.

 

@PDZ - Hi, what you are asking isn't going to need that - If you say game is "portrait only" you just limit "Player" settings to Landscapes, and then have one screen layout in vertical style.

Then there is DeviceOrientation - but I don't see why you would need this.

 

I think there may be a misunderstanding here. I am not asking how to limit the supported orientations of an application. I am asking, how can I design a UI prefab that will always display in landscape, regardless of what allowed device orientation settings the Unity project may have.