I think it could be argued that some global warming could be a net benefit for Canada. As long as it stays below the level that would cause global catastrophe. Sea level rise will cause some issues, but Canada really has very few large cities on the coast and there are (expensive) ways of dealing with that, just like all other coastal cities will need to do in the coming century. But on the other side of the equation it would extend growing seasons and increase the amount of arable and forested land in the vast interior of the country. Changes in rainfall will be a mixed bag, bringing adjustment, but likely not ruin. Maybe this is a very simplistic way of looking at it, but as a Canadian I've always selfishly looked at global warming and said "bring it on". Of course global warming could reach a point where it causes serious catastrophe on a global scale, e.g. releasing methane deposits on the sea floor and going into a feedback loop. That's a losing scenario for the entire planet, and there's no guarantees yet that we will avoid that fate.

Almost 40% of the US population lives near a coast.

http://stateofthecoast.noaa.gov/population/welcome.html

What's your guess to what part of the economy that represents? I don't think you thought this through. Katrina cost over $100 billion. The damage to the economy will be in the trillions. Put your million dollar CT home, put it on a truck to Montana, where it's worth 75% less?