There is no official canon viewfinder for the EOS M and options are very limited. I heard that you can use the Olympus VF-1 and Leica X-1. You can check out this persons thoughts http://thelazytravelphotographer.blogspot.com/2013/04/my-canon-eos-m-reviewpart-one.html.
You may be able o use a hotshot mounted 35mm optical viewfinder but pro by very old or as much ad the camera. There are also magnifying aids that you hold I've the screen. This s the only camera I have owned where I like using the LCD screen to frame nd that is because of the setting which trips the shutter after you touch the spot you want in focus.