Hi Coralie. I don't know the answers to all of your questions (I'm not sure if you need to tell Canada that you are leaving), but as for visiting family in Canada, once you have your Green Card in hand, this will not be a problem, and you will not need a visitor's visa. Info found here:
First, let me just say that visually the new VJ is quite pleasing, very "web 2.0." Nice job, the hard work shows. The bugs are a little annoying right now (especially reading history not carrying over between computers) but I'm confident they'll be worked out in time.
The reputation system, however, is a terrible, terrible idea. All it's going to do is turn Visa Journey into a less fun version of Mafia Wars. The fact that you can only mod a certain number of posts per day won't stop anybody, but it *will* encourage cliques to mob-mod, as well as encourage sock puppet creation.
Please drop the reputation system. The good that comes from it will be completely overshadowed by the bad.