I would highly encourage you to read [1] to get a better sense of the potential available in the North. The arctic is estimated to have over 22% of the world's oil and gas reserve [2]. Around 10-12% of the world's population is dependent on fisheries and aquacultures for their livelihood [3], so naturally, as fisheries become depleted in other parts of the world [4], the value of Northern fish stock (especially wild caught) is likely to rise. Minerals are already extracted all around the northern territories, an increase in temperature is likely to make some regions/zones economically viable, just take a look at Europe and China's race towards Greenland's potential rare-metal stock [5]. As a trade route, it can be considered one of the safest and fastest route to connect the East of North America and Europe to Asian markets. Just to give you a sense of how much money circulates in Trade Routes, the Suez Canal in Egypt hit a record revenue of $5.5billion in 17-18 [6]. Even if the northern region only becomes viable for half of the year, it may still be worthwhile, just look at other industries (think Tourism) that are on the same boat.
Countries have gone to war for territory and resources for millennia, if Canada doesn't position itself well to protect it, someone else may come and try to take it away from you. This can happen via fisherman/oilers invading your territory, among many other ways. Always remember, if you are not willing to take the risks and investment is potentials, someone else is and when they strike gold, you may only be able to watch it.
[1] https://en.wikipedia.org/wiki/Arctic_resources_race
[2] https://www.reuters.com/article/us-russia-arctic-insight-idU...
[3] Food and Agriculture Organization of the United Nations
[4] https://www.weforum.org/agenda/2018/07/fish-stocks-are-used-...
[5] https://www.nytimes.com/2012/09/19/science/earth/arctic-reso...
[6] https://uk.reuters.com/article/uk-egypt-economy-suezcanal/eg...