Canada may shift to becoming more nationalist as they are thrust onto the world stage, but the military here has absolutely 0 cultural impact and I don't see them shifting towards military rule. A reinstated monarchy sounds interesting, but is also pretty unlikely what with Quebec already not being happy as part of Canada (and as part of the British-Canadian Kingdom? Nope).
Canada, Brazil, Argentina, and Ukraine are probably the only countries capable of feeding themselves and exporting a lot of food out. Germany, France, Mexico, the Netherlands, and much of Southeast Asia will probably be able to get by relatively well. The rest of the world will be starving with the US, China, India, and Russia gone, though. In the immediate term, food is going to be a major concern which is why the more agricultural countries will see a dramatic rise in prosperity.