Countries can't sue countries. Countries can have businesses in a country and file a legal suit in the respected courts, but it would be the same as an American company suing the government. Even then, it's hard to sue the government regardless.

And by the time anyone could even try to form a class-action lawsuit the case would've already been thrown out in court. As much as we love weed, there has to be SOME justice when it comes to sticking to laws, otherwise no one would take the legal system seriously.