Based on my experience as a technician at Canon Australia for 5 years in the good old days (New F1's, T90, AE1 Program, Eos 1n, Rs, even the odd Leica mount Canon rangefinder) they use less than 5 microamps when they are on and just sitting there (my memory may be mistaken to the actual number as it's been 20 years), without any of the buttons being pressed. Funny thing was you could get the same sort of battery drain with the camera switched off with a button presses (strange-I know, but true..)

My usual advice is to leave the camera on while you are actually shooting, and turn it off at the end of the day when you put it in your bag....just make sure none of the shutter buttons (body or grip) are being pressed