This is, indeed, a hot topic. As one poster pointed out, the real purpose of the religious notation on the ID disc is to ensure proper spiritual care when unable to speak and, ultimately, handling of remains. It's a purely individual question, based on how you trade off care of your spiritual issues against the possibility of being tortured or killed for your religious faith. But, the tone of some of the posts here warns us how uncomfortable many Canadians are with the idea of faith.
While typical WASP, middle class Canadians with a liberal, middle of the road upbringing are generally quite happy to either have no religious beliefs to speak of, or to compartmentalize their "religion" into something they put into a box and take out for Christmas/Easter/etc ("CREASTERS" some chaplains call them...), an increasing number of Canadians today come from cultural backgrounds in which faith is an integral part of their life and informs everything they do. It instructs their code of morality, their concept of justice, and perhaps even their attitude towards war. This includes, in particular, Muslims and non-European Catholics. IMHO if this is not what your faith does, why bother?
I am an Anglican (not really a "Protestant" but in fact a kind of "Lost Catholic") but my wife is a devout RC. Although I am a rather wretched excuse for a Christian, in our 21 years of marriage I have attended Catholic churches with my family all over this country (and in the US). They are almost always full, and to an increasing extent the congregations are made up of new Canadians. Now, going to church does not, IMHO, make you a Christian, but I argue for a strong correlation between attendance and faith.
Anyway, in the end, your faith is your business, but let's not belittle the power and importance of anybody's beliefs, especially for those of us who must face the dangers and spiritual/moral challenges of our profession of arms. And that old saying "There are no atheists in foxholes" has been repeated over and over by soldiers for a couple of generations now, so there may just be something to it. Cheers.