I prefer to avoid the pris module altogether, its mostly unnecessary for use with python.
Instead, you can achieve this with 2 lines of code.
import lwsdk
lwsdk.command("TopView")
Replace "TopView" with your preferred orthographic angle.
EDIT: I realize you might have been referring to the *type* of camera, not the viewport. I'm not aware of a command that lets you change the camera type directly and I don't see anything in the C documentation which references that you can do anything with the camera type or the properties specific to that type (if applicable). You might need to use a template object using load from scene as an alternative.