"He makes the crossing of the ocean easy."
Translation:El face traversarea oceanului ușoară.
"Easy" is correct, as it's modifying the noun "crossings", as can be seen from the use of the adjective "ușoară" in the translation. The adverb "easily" would be "ușor". The meaning presumably being that while others may make it difficult he makes it easy.
However, I think a better sentence might be:
"He makes the ocean crossing easy"