It's a good question, Capt. CM tried it a while back, YCAB to YLRE direct, and the comment was that being outside ssr for so long they required via TAM.
Mr Conrod seem to have the same experience, as I do, such as YCAB to YMOR DCT even if planned via AMB and the airway, some times it is better for them also to give you direct, it may mean less crossing traffic issues in the terminal area.
J
