All the signs seem to indicate that he did: including an admission from the Cardinal himself. My friend at Les Femmes commented on a biography of the pope and highlighted some of the goings-on before and during the conclave. I post below a video of an address that McCarrick gave at Villanova University in October 2013. I urge you to listen for about 5 minutes, starting at the 17:00 mark. I believe that McCarrick did in fact "talk up" Bergoglio. Recall the address that he gave prior to the conclave, in which he voiced the opinion that the next pontiff should be Latin American - or at least familiar with the church in that area.
Did Cardinal McCarrick violate canon law? I'm not sure. The electors themselves were forbidden to do such lobbying, but McCarrick was not an elector owing to his age. However, Cardinal Wuerl was an elector and was in the conclave; they both are peas from the same progressive pod. Might this little tid-bit explain why Wuerl wielded such influence at the sin-nod and why he was allowed to supplant Cardinal Burke in the Congregation of Bishops?