It sounds to me like you're wanting to use the "+" and "-" buttons on the back of the camera to electronically zoom in on your field of view. That is not what these buttons are designed to do. They are used to zoom in when reviewing images on the LCD screen in playback mode that you've already taken.
I think you'll also find they can be used to zoom in on the LCD as a focusing aid while composing your shot when shooting in Live View mode. But the image recorded by the camera will be taken at the actual focal length setting of your lens. No DSLR has any kind of electronic zoom function.
Your focal length is strictly determined by the lens and possibly by the use of a tele-extender between the lens and the body. It sounds like the "older Canons" you mention were probably fixed lens models. They would have had zoom controls that would actually mechanically move the lens mechanism to change the focal length.
Spend some time reading thru your user's manual and you'll find lots of other useful features that didn't exist on your fixed lens cameras! 😉
