Ates,
In the JFBConnect configuration area, there is a setting for "User Creation". If you have it set for "Full Joomla User", that will bring the user through the registration process where they can set their own username/password. If you change it to "Facebook User Only", the account will be created for them automatically like you're looking for.
LinkedIn, however, will require the user to put in a username/password. That's simply because LinkedIn does not allow retrieving the user's email address from their system. Since Joomla requires an email address, we need to ask it from the user. So, with JLinked, there will be a small registration form that will need to be filled out. In the next release, we'll be adding options so that all the user would have to add is their email address and JLinked will automatically create a username and password, which will make the form extremely short. We can help you do this now if you'd like that.
In both cases, after the account is created (either automatically with JFBConnect or after the short-form with LinkedIn), any other profile information can be pulled automatically into your site.
As for the Canvas setting, it sounds like you have something in your template or a plugin which is sending a specific meta tag which prevents the page from being loaded in an iFrame. That's a common feature in some SEF and security extensions. You'll need to disable that.
Hope that helps,
Alex