All meta-data about images stored in encrypted form. To view them, just by looking in the document properties, it is impossible. You will have to use special software. And for each manufacturer's cameras to look for its program.
Let's start with Nikon. To view meta-data, you can use the program ShowExif. It weighs less than 1Mb and requires no installation, what is very convenient. Just run the program. In the left window, specify the path to the folder with the latest photos. In the middle - will appear in the photos themselves. Select the last one. In the right window will show all the meta data about the picture. Among them, almost at the end look for the line "Total Number of Shutter Releases". The figure in this row is the number of the last shutter. If it says 50, it means your mileage is 50 frames. If written 23824, then the shutter of your camera clicked just enough time.
As for Canon, everything is complicated. Most people recommend with cameras of this brand to contact the service center. They argue that the only way you can determine the mileage of the camera. However, there is a chance to learn meta-data and samostoyatelno using the program EOS Info. The program's interface is almost the same as ShowExif. However, it should be borne in mind that the program can read data only on certain Canon cameras. There is also a chance to get meta-data through ShowExif. Sometimes it works. Apparently, it is difficult to come to a specific conclusion. And you better do with the camera to go to service center and get accurate data on mileage of your camera.