I would expect that if the Germans were making a determined attack on the line it would have proved not only breechable, but would have ultimately failed in purpose. I would list the reasons as:

The Germans had developed weapons capable of dealing with the fortifications. These include the 80cm railway gun, 54 and 60cm mortars (Karl), high velocity large caliber guns (eg., 8.8cm and 10.5cm AA guns among others). The former were capable of penetrating most of the defenses in a traditional sense of just hammering them with fire.
The AA guns could take on the defenses in a way the defenders had not foreseen. That is, the Maginot Line was designed to be a series of mutually supporting positions built primarily on reverse slopes and with little firepower that projected into regions forward of the defense line. Instead, artillery fire into the enemy lines was to be provided by conventional field artillery to the rear of the line.
This means it is possible for the Germans to bring such guns forward to positions were they could easily take out the cloches used for observation and fire control that were exposed blinding the defenses.
Another problem with the line is that it lacked any mines along its length. The defense positions forward relied on just wire and anti-tank obstacles for passive defense. Again, these could have been overcome easily by artillery fire alone.
Once the line is breeched the French would have still proved inflexible and unable to cope with a fluid and rapidly changing situation. Their doctrine of methodical battle was a massive failure of policy.