The main thing we'd lose is the autonomy to manage our own economy. Given that's something we've handled especially well resulting in impressive economic stability in spite of global events, it's not a thing to be sacrificed lightly - or at all.
The main benefit of joining the Eurozone is tight economic integration that lets member nations share the larger group's economic stability. That benefit is never going to substantively materialize for a nation physically separated by an ocean. But we'd still be losing the right to decide how many power coupons we print, directly regulate our own banks, and set interest rates/inflation targets.
I'm open to other forms of EU association, but the Eurozone is a solid hell no.
Good.
Let him stick to that line, keeping Canadians angry and trade negotiations stalled. He's helping us maintain the momentum needed to build a stronger Canada and end reliance on U.S. trade for good. When he and his ilk are all eventually deposed, the U.S. will have to make many concessions to get (partially) back into our good graces. If that doesn't happen, our need for political separation will only increase.
No deal is the best deal.