Why the St. Lawrence Seaway is not called a canal

Why is the St. Lawrence Seaway called a seaway rather than a canal?

Because it combines canals with navigable channels instead of forming one continuous canal, and the distinct name helped present the system as something new.

The St. Lawrence route is a mixture of constructed canals and navigable natural channels, rather than one continuous canal. Calling it a seaway distinguishes that combined system from earlier canal projects. The name also gave the new route a separate public identity. Its terminology follows both physical structure and presentation.