Enough of these flippant replies to your serious research enquiry. There is no Criminal Code—we are taliking Canada, yes?—offence of "Asking Someone to Pose Nude", nor is there a provincial or other health statute, nor a Toronto bylaw requiring you to take out a License to Ask Someone Anything before you do.
Far from it, and if "…she run [sic] screaming to the nearest police", she's in danger of being charged with disturbing the peace or some such.
So go ahead, select a babe, study her carefully over some time to make sure she's photogenic, then march up and say, "Strip and I'll shoot you. With my camera! Just a joke to put you at ease. Har Har! No, but I really mean it, see my camera. And I won't even joke about using my really long lens. Oops! Double Meaning Alert! Really, I just want to snap your double meanings. For free! Hee Hee".
Nothing in there that approaches 'communicating for the purpose' even if you did show interest in what she had undercover.
But to be on the safe side: Don't offer money. Go for it.