From what I understand, you can get to Cuba from Canada or Mexico if your point of origin is the US. I would love to go to Cuba but I'll pass until it's legal - if caught, I'd face loss of my job, and prosecution and hefty fines.
Although I live in Japan, and have never been to Cuba, I too would go with Cuba. I agree with the others that it's probably going to change quite a bit in the future. Japan will continue to be the concrete jungle it is (yes, there are oases of beauty, but not many). September is still typhoon season and it will be incredibly hot and humid.
My favorite thing is to go where I've never been. D. Arbus
I would go to Japan. In the USA they seem to think Cuba is so exotic because they don't go there... but everybody else goes there. In eastern Canada it's a very popular spot and I know people who have been half a dozen times in the last few years.
I just looked up a flight... you can fly Toronto to Havana and stay for 7 days. Flight, pickup at the airport and hotel. It was under $400. I guess that's why everyone goes there.
I plan to go myself.... I'm just waiting for my next batch of test cameras from Sony and I'm out the door. To me Japan would be more exotic.... but too costly if I'm just testing cameras.
I'd go with Cuba. I know Steve personally and he's a great guy. A bit intense at times but a great guy. I also have a thing for Latin America sites. I've visited Mexico several times and how knows maybe retire somewhere south.
"We are what we repeatedly do. Excellence, then, is not an act but a habit"
I say you can always go to Japan, and it will be Japan. Cuba OTO may change dramatically, or your ability to visit it may be even further curtailed by the government. (Don't get me started on the "land of the free", except, unless, but...).
Or Cuba may become suddenly "open" to the US. Given our close proximity it won't take long for us to wreck it.
I'd go to Japan. I find it's rich history and such to be very interesting. I don't see what fascinates people about Cuba, I think that a lot of the excitement over it is that we aren't allowed to go. Going to Cuba seems almost exploitive to me. I do appreciate it's historical significance but it's kinda of like "hey! there's a place where everyone is poor and it's like it's 1952 because of an oppressive quasi-monarchal government is in place. Let's go take pictures of them." Buy Steve McCurry's excellent book on the subject and read it on your flight to Japan.