What is the key difference between the Suez and the
Panama Canals?

Because the Suez Canal is situated at sea level, its draft (depth) varies with the tides. The Panama Canal is made up of a series of locks that lift the ship to Gatun Lake's level (26 meters above sea level).

Explanation:

The Suez Canal is unique in that it is a sea-level canal. That is to say, no device is required for a ship to cross the canal from one side to the other. It only needs to enter, sail through, and exit. It was built over a ten-year period under the direction of the vicomte FDL.

De Lesseps attempted to create a sea-level canal in Panama, but it was deemed impractical due to the difficulty of c)tting a channel through the mountains that straddle the Isthmus of Panama. As a result, the Panama Canal might be thought of as an elevator canal. The difficulty was overcome by flooding a mountain valley and erecting elevator locks that raised the ships 26 meters above sea level before lowering them on the other side of the mountains. It took 33 years to construct.

TL;DR Ships travel through an artificial cut in the earth in the Suez Canal. Elevators in the Panama Canal transport ships up to a mountain lake and then back down.