How do I change the View Port size?

I am making a game with single player and local, keyboard multiplayer. The single player has a view port size of 854 x 480. The problem is that I want the single player to be that size but the multiplayer to cover the full layout as there are two controlled characters.

Is there a way that I can change the view port size with code or make it split screen?

Thanks.

You should not alter the layout's canvas size to do split screen.

From the top of my head there are several ways to achieve splitscreen:

1) Put each player's viewport on a separate layer, then sync objects and offset positions.

2) Use n drawing canvases, then iterate through each player and paste that player's viewport to their canvas.

The system action Set canvas size can change the viewport size, but you don't have to use it to display an entire layout - you can do that by changing the layout scale instead.