At no point is the EU "given" power, nor is it taken. However, in the interests of the union in general, many of these treaties have non-negotiable requirements.

If you watch the history of the EU and its predecessor and you will see that the EU became more powerful. It started with a coal and steel union and now it is a defense, free trade, law, financial, and securing democracy partnership. Of course this was implemented because the members wanted it, but I think this will end in a United States of the EU. I do not have a problem with it, but many people (especially the people that are political disenchantment) would not like it.

It is highly unlikely that membership in the EU would automatically include membership in a defence union.

The European Parliament discusses this topic because of Manfred Weber the chairman of the biggest group EPP. Weber showed its interest in this topic in the German political talkshow of Martin Lanz. The biggest advocate of a European army is Macron the French president. He does have a other view of a European army as Weber, but after trying to create a more European army structure for many years he signaled to be willing to talk about it.

Canada would have seats in the European Parliament, respresentation in the the European Commission, and would therefore have some influence on things like interest rate policy.

That is true but the European liberals Renew Europe are not the biggest group in the Parliament. Macrons party lost so many voters to Le Pen (right extremist). The German SPD and Greens lost many voters to the conservative parties. Sweden and Austria shifted to the right as well. The parliament shifted to the right and I think it would not be changed by the Canadians EU election results. The new Icelandic government has now announced that it will hold a referendum on the issue of EU membership by 2027. The polls in Norway becoming more and more positive about joining the EU. This could shift the EP to the left and the centre.

They've bullied our government, crippled our industries, and even killed national projects like the Avro Arrow, and yet we still think of ourselves as "independent".

I do not have enough knowledge about the Canadian history of politics.