Seeing as Sweden was actively planning an amphibious assault into Denmark to deny it to the Russians, it's a safe bet the Swedes would also pre-empty any move against Norway, and in that case they would also have the assistance of the 15,000 Norwegian Rikspoliti they had been quietly training since 1943 for when the day came. In fact 1500 or more of the Sweden-based Norwegians took part in the Russian liberation of Finnmark, together with UK-based Norwegian forces, the whole of the county having been liberated by VE Day.
My great uncle picked up a Norwegian medal for being part of Operation Doomsday, the 1st Airborne Division airlift into Norway to handle disarming the Germans and rounding up Quislings with the Rikspoliti. If Doomsday wasn't feasible in the face of Festung Norvegen, there were several plans to combat drop the whole of 1st Allied Airborne Army (8 division equivalents) into the rear of German forces in 1945 that would have been much more feasible against a static defence in Norway than the fluid front in Germany that meant the planned operations never came off. In fact Operation Effective was specifically designed to prevent the creation of Alpenfestung, so pencilling in 1st AAA to deal with Festung Norvegen is entirely appropriate.
The problem for any idea of Festung Norwegen is that while significant parts of Norway are rugged enough to favour the tactical defence, the country is wide open to the strategic offence from the East - Sweden, and the West - amphibious operations across the North Sea. The terrain might not suit mechanized operations, but it would be next to impossible to defend against Swedish/Norwegian ski/mountain troops or Allied commando operations. It's very easy to envisage a joint Allied/Swedish seizure of Narvik cutting the country in two, with narrow defensive fronts - under a mile at one point to the south of Narvik IIRC, able to be held while a break-out force is built up within the beachhead. Match that with cross-Baltic amphibious operations, Swedish incursions all along the frontier, including large-scale conventional operations in the south, plus the potential use of 1st AAA, and the German defensive problem is a nightmare.
