They are tariff-free. We don't have tax measures or rate measures that interfere with these interconnections. What we have, primarily, is policy measures. For example, the 1995 federal review of interprovincial trade had a chapter on energy. It was left blank. This is an illustration of the kinds of things that have interfered historically with better electricity interconnection among provinces.
On October 2nd, 2017. See this statement in context.