I will rarely play Devil's Advocate in that sense [though I have done so at thesis defenses, where the candidate needs to demonstrate the ability to support his view however correct].
But I by nature look at all sides of an issue, constantly checking to see whichthe data most strongly support, and if you say the sky is blue I will bring out the fact there is in fact no blue pigment, it is all in how the atmosphere affects light of different wavelengths. If you tell me the sky and the bluebird are actualy NOT blue [even if I just got through saying that to Joe over there] I will argue that "blue" being a category of human language, is most appropriately evaluated as perception regardless of the object, that our eyes are in fact receiving blue light.
Both of which are corect positions supported by the data, which way I lean NOW depending on how I weight the factors, and either position or both may be swept away by one new datum received.
This is not quite the devil's advocate stance you describe, but of course it is precisely the task of the advocatus diaboli whose function is not so much to argue as to ensure that ALL the data in the case of proposed canonization are brought forward and discussed.
Note by the way the assumption in the title that the candidate OUGHT to be canonized.