"Is this class easy?"
Semantically they both mean the same here.
Syntactically, they also both take a copula in the polite form here. If it was informal, however, you could not put "da" after yasashii, only after kantan.
It's a bit complicated but Japanese doesn't have adjectives per se. "adjectives" that end in "i" act like verbs. Other "adjectives" are nouns that can modify things if you add "na"