plain sailing vs easy going

plain sailing and easy going both are nouns.

Word	Noun	Adjective	Verb	Adverb
plain sailing	Yes	No	No	No
easy going	Yes	No	No	No

As nouns, plain sailing and easy going are synonyms defined as:

Other synonyms of plain sailing include clear sailing.

plain sailing (noun)	easy going (noun)
easy unobstructed progress	easy unobstructed progress