Do stunt actors look exactly the same as the real actors?

 Reasonable. This is an example of what I mean.

Here's Priyanka Chopra with her replacement actress, Aja Frary:

Here's Chris Hemsworth with his stunt double, Bobby Holland Hanton:

Here's Ben Affleck with his replacement actor, Rich Cetrone:

Here's Reese Witherspoon with her replacement actress, Marilee Lessley:

As you can see from this example, they don't look exactly the same, but they're good enough to fool the camera.