The CARs and the (very vague and broad) written exam guide are on the Transport Canada website.
It's not like the US - the questions are not published. I'm not aware of any test prep books specifically for the conversion exam, but they may be out there... failing that, you could get the full ATPL books from Aerocourse, which may help in the studying. (Might be some other ideas on the avcanada forums, not sure.)
I have heard, and am not surprised, that this exam is one of (if not "the") most failed exam at TC.
Good luck.