R.v. Barros, 2011 SCC 51 has some useful language regarding directed verdicts:
A directed verdict is not available if there is any admissible evidence, whether direct or circumstantial which, if believed by a properly charged jury acting reasonably, would justify a conviction: R. v. Charemski,  1 S.C.R. 679, at paras. 1-4; R. v. Bigras, 2004 CanLII 21267 (ON CA), at paras. 10-17. Whether or not the test is met on the facts is a question of law which does not command appellate deference to the trial judge. An error of law grounds a Crown appeal under s. 676 of the Criminal Code.