Is there any case law where a client’s confidential information was disclosed to the solicitor prior to the formation of the solicitor and client relationship?

As for the submission that the document pre-dates the formation of the solicitor and client relationship, that is debatable at best because it could equally be said that it evidences the formation of that relationship. The point is moot in any event, in my view, because the privilege does not come into effect only after negotiations leading to the relationship are finalized. If it did then the client would be deprived of the privilege at the very time when it is most needed, when he or she is explaining the legal problem to a prospective lawyer. Moreover, if the client who decides not to retain a lawyer to whom he or she has revealed confidential information is not protected by the privilege then its usefulness would be severely undermined. In my view the privilege comes into effect “as soon as the potential client takes the first steps, and consequently even before the formal retainer is established.” See Descoteaux v. Mierzwinski 1982 CanLII 22 (SCC), [1982] S.C.J. No. 43; 1 S.C.R. 860.