Hi, if I remember the order of countries at the World Showcase, on the left side (when facing the American Pavilion) the first country is Mexico and the next on (moving right) is Norway. So most likely they will let you in and you will walk past Mexico to Norway and then (if the World Showcase isn't open yet), you will have to leave the same way that you went in (back past Mexico).
The International Gateway is all the way on the other side of the World Showcase, so you would have to walk all the way from Norway, back the way you came, all the way around the lake and then past Canada and England to get to the International Gateway and the boats to go to MGM.
At this point, I would think it would just be easier to walk back to the front of Future World in Epcot and catch a bus to MGM, as the walk out of the World Showcase and around the lake would probably be much longer than to the front of the park.
If the World Showcase were open (it didn't open until noon when we were down there last year, so I am not sure if it is opening at 11 or noon now), then it would be a bit quicker to walk through it and out the International Gateway. But since you have to backtrack anyway, I would go to the front of Epcot and take the bus to MGM.
Have a wonderful trip!