The site below has pretty good pictures of infected branches cut off.

The only thing I might question is the suddeness of the dead branches. Usually plants with a wilt disease show symptoms of wilting, flagging and early defoliation the previous year at least. How did the tree look last summer? Dieback could occur suddenly if the infection is severe enough. Dieback over the winter could occur for other reasons such as drought or severe cold.

I don't know if such a thing exists in Canada, but many of the state universities have plant disease clinics that can positively diagnose the disease. It costs money, but if this is a valueable specimen it might be worth the costs of a proper diagnosis before removing it. Also, if it is VW, then you'll have to search for replacements that are resistant. As far as I know, there is no cure for VW. Just treatment of the symptoms by pruning out infections and maintaing the vigor in the plant.

Here is a link that might be useful: Verticillium in Maple

Verticillium wilt is very prevelent with Japanese maples in the PNW and most experienced nursery folk can identify it rather readily. The dark cambium and streaking under the bark are very characteristic of this problem. And the action of the wilt can take various forms, including not leafing out in spring. I would say more often than not that obvious signs of wilting with JM's are superseded by complete failure, often in just a day or two.

Saving the tree is speculative at best. Removing the affected section may help (sterilize any pruning equipment before and after each cut), but since this is a root pathogen that affects the vascular system, it is very likely the root system is already compromised beyond salvation. Keep the tree stress free and hope for the best.

I also think a positive identification is merited, because if you want another J.M. this one, if it is infected with Verticillium must be dug up with as many roots as possible and then burned. I don't think any copper solution will kill this fungus.