Of course they are!
Think about it, they migrate thousands of miles each year, they know very well about currents and geology; they have a complex communication, they defend other species from predators, like dolphins, sea lions and even humans! They sing and memorize 45 minute's songs, they interact with boats, displaying all kinds of acrobatic behaviors, whales learn all they need to survive in their first year.
Whales are social animals that live in large groups. They adapt easily. Whales have several strategies to catch their prey, like bubble netting. They organize with other individuals to form a feeding
group where each individual has its own role, so they work in teams.
Whales and dolphins contain specialized brain cells called spindle neurons. These are associated with advanced abilities such as recognizing, remembering, reasoning, communicating , perceiving, adapting to change , problem-solving and understanding. Well, then whales are pretty smart!
And a huge animal like a whale that is so gentle is enough reason to me, to believe they are intelligent!
Oceanologist and whale watcher.