Unless Tolkien addressed this in one of his letters (I really wouldn't be surprised), we don't know for sure, but my guess would be that Sam's resistance was mostly temporary. He could carry it for a short while without succumbing, and he could be around frodo for the whole journey with no issue, but he'd have eventually succumb to it.

Also worth noting that it's heavily implied that the whole thing was predestined by Eru, and so with that in mind, it makes perfect sense that Frodo carries it instead of Sam, because

A) if Sam carried it, it's unlikely he would have trusted Gollem, and his "help" was required in several ways to get the job done

B) Frodo being the carrier + Sam as his sole ally, while not intended by the council of Elrond, turned out to be a formidable match, thanks to Sam's resistance to the ring and his loyalty to Frodo. Idk if when push came to shove, Frodo would have been quite as loyal to Sam as Sam was to Frodo (not with the ring doing it's thing afterall.

Its also worth noting that Tolkien had some kinda weird views about the whole "servant & landed gentry" dynamics, as can be seen in just about every dialogue between Sam and Frodo lol - Sam being the effective leader, despite being a humble gardener and Frodo being basically a Lord in hobbit terms isn't something Tolkien was likely to write