Bob, you are (mostly) right. You are absolutely right that police will arrest you. I do not know about Canada, but here, in "the land of the free," most judges will then let you go.
You see, only about 10 states here have a specific law banning up-skirt photography (as of 2005, at least). There are some judges who specifically said, in a freeing verdict, that women do not have "a reasonable expectation of privacy," even under their skirts
, if they are in public. A USA Today article on the subject here
Expectation or right? Different, very different. If they legally don't have that right then the law is truly an ass (no pun intended, in this case). A charter for violation of the person, then?