It may just be that my passport is from the U. S., not Canada, but I don't think that Customs Canada has ever checked my items, and if asked, I always just say that they came with me from Canada and that they are returning with me. Six years in Canada, crossing the border at least three times (each way) a year, and I have yet to have any issue--even when I actually was importing over my limit, and declared it, they still didn't seem to care, and never issued me duties. Now, I am traveling with two Digital Rebels, four lenses, and a bunch of computer stuff, so perhaps if you have obvious professional-grade gear this is different.
Now that I know about the form, I will probably fill it out just to be safe.