Only way that is happening is with Link fully armed and Cloud with no materia. Cloud is superhuman at his base self, his Lvl. 3 and 4 limit breaks are brutal, and he just gets worse with Haste, Reflect, etc., never mind offensive spells like Ultima, Comet, summons...
Link is resourceful, he may outwit Cloud and I think he is genuinely smarter, but he will absolutely not beat him in a straight fight. Just not happening.
Maybe? Its highly dependant on a lot of factors. If Cloud can use healing items and magic, then does that mean Link can use fairies? If thats the case, then Link would technically be immortal.
Death Battle did two episodes on the matchup, with each of them winning once. Link won when he had all his items and Cloud could use materia but couldn't use summons (they were considered outside help which was against the rules in DB at the time). They said Link's massively varied arsenal more than made up for Cloud's pure strength advantage. Rematch, they added Link's abilities from BotW and gave Cloud his summons back, and Cloud won, with the pure overwhelming power of the summons, of course.
Oot link could probably win using a bottle and a stick or something. Or maybe play the bottle like an ocarina and pick up some grass while getting exploded and slide around and some other shit then warp straight to the credits.