Patricia,
If I remember correctly one "problem" with some of the older Canon MX models was that scanning would not work via wireless connectivity. Not sure about faxing per se but I think that also did not work wirelessly.
I had that problem (just do not remember the specific MX model) and also found wireless printing to be much slower than wired (ethernet).
Dig into the manual and Canon's FAQs. Canon, of course, does not go out of the way to make full note of that. But it is there somewhere.