You can automate exposure compensation with Autoexposure bracketing (AEB).
It takes three shots in quick succession, each with a different amount of compensation. You can start with the default setting of the camera and add plus and minus compensation at selectable levels (-1, 0, +1, or -2, 0, +2, for example).
The exposure value (shutter speed or aperture) that changes with the compensation depends on the shooting mode set. With Shutter-priority (Tv), the aperture will change; with Aperture-priority (Av), the shutter speed will change. Either or both values can change in Program AE (P) mode.
AEB is particularly helpful if you do not like the correct exposure but are unsure of how to change it. However, it does have another application; High Dynamic Range photography.
High Dynamic Range (HDR)
There is a limit to how much of the dynamic range in a scene that a digital sensor can capture. If you want detail in bright highlights, such as the sky, you will probably lose detail in the darker shadows. Adjust the exposure to capture the detail in the shadows and you will probably lose it in the highlights.
One way to overcome this limitation is to take two or more pictures at different exposures and merge them into a final photograph. This increases the dynamic range and makes it possible to show detail in the highlights and shadows at the same time. This is called High Dynamic Range (HDR).
You can create HDR images in Canon's Digital Photo Professional (DPP) software. First shoot three images using AEB, try -2, 0 and +2. After transferring the images to a computer, open DPP. Under the 'Tools' menu item, choose 'Start HDR tool', select the three images and click 'Start HDR'. The software will then present you with the merged HDR image, with sliders to adjust brightness, saturation, contrast and several detail enhancement options.
Newer EOS cameras feature an 'HDR Backlight Control'. When set, the camera automatically takes a series of images at different exposures and merges them into a single image. The result is a photograph with good detail in highlights and shadows. Some models also allow HDR in-camera; letting you control the dynamic range. Check your Instruction Manual for details.