Canadian expats registered with embassies is a difficult figure to come across. I've contacted over 150 different missions abroad. Due to the inability of the embassies to provide that information because of privacy laws, I don't have accurate numbers as far as registered numbers.
The Asia Pacific Foundation of Canada estimates the number to be in the neighbourhood of 2.7 million Canadians. Based on the estimates that the Canadian missions have given to me—they haven't given me registered numbers but have often given me estimates of the number of Canadians who live abroad—we come to a figure that is close to 2.5 million.