I own a Canon WD-H43 wide converter lens that is made specifically for this camcorder, and a few others. It is a very high quality lens and works perfectly with HF M500. Its quite large and heavy, not a problem for me. Unfortunately expensive around $200. I'm guessing it increases field of view maybe 15 to 20% not a lot but has allowed me to get some great video I otherwise couldn't have gotten.
The Canon VIXIA HF M500 can take 43mm lenses. The main lens is threaded, but make sure you read the specs on the lens you are buying, if in the description there is no thread size do not buy that lens! Once again make sure the lens is for 43mm!!