They are looking for what is called "objectionable material". I don't know about Canada but in Australia it would be importing porn, any CP-like looking things (say porn with young Asian females that look like children and they have no means to check their age) and so on. I don't know full definition but basically they can add and remove stuff to this "objectionably material" list. Possessing data listed there is a crime. Recently, in New Zealand the shooter video go onto that list.