In my webpage, I have half of it being a map display using Google maps. What aria-role should I add to that canvas element which is displaying the
Is a Google Map something accessible for blind people? No.
The answer to that question give you some clue : give it the presentation role and aria-hidden=true attribute. You should give a correct replacement for the missing information like a full textual itinerary if your map describe an itinerary.
Eg:
Visit us at our store, Penny Lane, 22, Liverpool
Liverpool City bus, Line 3
Note: Widget is an abstract role you can't give to an element.
EDIT: This will remove the ability for a screenreader to interact with the canvas, both from keyboard and mouse, which may not be suitable for illiterate people using a screenreader for instance (when the canvas has better accessibility features than Google Maps'). If you really want to give access to an accessible canvas, do not change the native semantic, otherwise, in this case, place a link before to jump the canvas, specifying that it has very uninuitive keyboard support and may not work with the mouse.