I researched this question when I was trying to get some G43 magazines from Numrich. As far as I could tell, and there were three or four directly related documents, the answer is yes and no.
Yes, you can import just about anything (like the other guys have posted), but CBSA doesn't have the technical knowledge to measure 1,3,5 or 15 round capacity. They are busy people and pass anything remotely controversial to the RCMP Forensics labs. They are busy too, and would prefer to destroy shady looking imports than make a mistake.
So to avoid recklessly endangering the Canadian public (smirk and wink), CBSA's regulations will permit imported high capacity magazines that have been welded to a zero capacity. No pins, bolts or other attempts. Welded shut.