Hillary was an incredibly weak candidate, and just about anyone on the GOP ticket could have beaten her. Now, they may have done it differently than Trump (e.g. the hat trick of Wisconsin, PA, MI is a uniquely Trump phenomenon). I have a good number of left-leaning friends that said they would have voted for any Republican except for Trump (a few said Cruz or Trump).
I will say that I do not believe Jeb Bush could have beaten her. I don’t think he could have gotten the strong border crowd to vote for him and so he probably would have lost because he was too much like Hillary.