It is indeed a gray area contingent on convincing a person you won't overstay (in the short term). As you build your case, it may help to read up on the rules on dual intent http://www.cic.gc.ca/english/resources/manuals/bulletins/2009/ob131.asp
Read the whole thing, but a couple of selections follow for easier discussion in the thread:
"A22(2) states: “An intention by a foreign national to become a permanent resident does not preclude them from becoming a temporary resident if the officer is satisfied that they will leave Canada by the end of the period authorized for their stay.” Dual intent is present when a foreign national, who has applied for permanent residence in Canada also applies to enter Canada for a temporary period as a visitor, worker or student. Dual intent on the part of the applicant is therefore not prima facie grounds for refusal of temporary resident status."
"An applicant applies for a temporary resident visa (TRV) to visit Canada but is denied solely because they have a family class application for permanent residence in process. In the refusal letter, the officer states that because the applicant is pursuing permanent residence, the officer is not satisfied that the applicant will leave Canada at the end of the period authorized as required by A20(1)(b). The officer has made an error. A22(2) precludes denying an application for temporary status on the basis that there is an outstanding permanent resident application, if the officer believes that the applicant will leave Canada at the end of the period authorized for their stay. If the permanent resident application is finalized after the issuance of the TRV, the applicant would be authorized, on the basis of the permanent resident visa, to remain in Canada."
This old thread may also serve as inspiration for a bullet-proof application: http://www.canadavisa.com/canada-immigration-discussion-board/invitation-letter-critique-svp-t42694.0.html