Well, Montreal has a long history with the petrochemical industry. You may or may not know this, but there used to be at least five refineries on the Island of Montreal. Now there is only one, operated by Suncor. There is an extensive tank farm that is actually the distribution hub for all of eastern Canada and part of the New England area as well. Petroleum products, or liquid bulk, represent about 16 million tonnes out of the 40 million tonnes that will be handled at the port on an annual basis. It is a substantial amount of traffic.
Don't forget, also, that there's another refinery in the Quebec City region on the south shore of Quebec.
I don't know exactly to what extent your question was about restricting tanker services, but doing that would be an issue.