To answer your first question, concerning which standards take precedence over others, I would note that a standard is a mechanism designed to facilitate the transfer or exchange of products. The buyers, who determine where the product will be used, are always free to request whichever standard they want. Whether it be the ISO standard in Canada, the ASTM standard in the United States, or the CEN standard in Europe, it is the buyers who know what product they need and where it will be used.
This is also true for Canadian buyers. For example, a buyer who wishes to import a product from Europe for use in northern Quebec needs to refer to an appropriate standard to ensure that the product will work during a Quebec winter. In this way it is the buyer who determines which standard has precedence.
As for your question on protectionism, this is a major factor. These standards are established by committees of the Canadian General Standards Board. It is essential that standards do not become a barrier to commercial trade. Any standard that might be perceived as being limitative or protectionist in a given industrial sector will be the subject of many discussions. Generally speaking, the members of these committees will ensure that the standards will not act as a barrier to trade.