The Corona simulator screen size is based on the skin you choose. If you want a 1920x1080 skin, you can pick one of the GameStick or Ouya skins. Those are as generic as you can get for that size. And they also have a 1280x720 version too. You can use the iPhone 5 skin to simulate the 1136x640 size.
Yes, with a background that bleeds, you have to assume that some of the top and bottom edges may get trimmed on some devices and on some other’s its the left and right sides that get trimmed off. Look at this image:
On an iPad you will get the blue and yellow areas. The red and green will be cut off.
On a 16:9 device you will get the Red and Blue area and the yellow and green will be cut off.
On a 3:2 device like the old iPhones and other 320x480 shapes you get the blue area only.
Assuming your background is centered of course.