Is there any case law that supports the argument that the use of evidence that could not have been obtained but for the purposes of the trial was unfair?

Firstly, the evidence in question did not emanate from the accused and thus did not point to unfairness of the trial process. In Leclair and Ross v. The Queen (1989) 1989 CanLII 134 (SCC), 46 C.C.C. (3d) 129 (S.C.C.) at 139, Lamer J. (as he then was) said: "I am of the opinion that the use of any evidence that could not have been obtained but for the participation of the accused in the construction of the evidence for the purposes of the trial would tend to render the trial process unfair." Here the Appellant had no involvement with the construction of the subject evidence. I emphasize that this factor is by no means solely determinative of the fairness of the trial process, particularly in this case wherein the subject evidence involves a co-conspirator.