Required entry visas

You need a double-entry visa. Hong Kong, as a special administrative region, apply different exit and enter controls from Mainland China. In visa area, Hong Kong is regarded as a foreign country, once you enter Hong Kong then return to Mainland China, it is regared as a new entry.

First entry: enter Beijing
second entry: enter Shanghai from Hong Kong

Canadians are exempt from a visa to Hong Kong for up to 90 days, so you don't need a visa to Hong Kong.