The fuel return line is continuous to the tank, not connected to the vapor canister. There should be a hard line running along the left side frame rail and ending very near the canister. If it is open I suggest that it is cleaned out prior to using it. You will find that a rubber hose is connected to it at the aft end and that is where I would cut and allow access for cleaning it. Once you make that connection be sure to watch for leaks.
If the first section of the return line which runs near to the filter and then avoiding the intake/exhaust manifolds is missing you should bend a new one.
The air bubbles that you see are a common occurrence with each pulse of the pump. That is the reasoning of the dual output filter's orientation with the return in on top of the carb fill line.