Rubio, I'm not certain, but if he pledges it I'd consider voting for him.
Cruz, I'm certain he'll take steps to control the border. If a physical wall is the best way to do that, then it'll happen if he has a GOP Congress to support the legislation. But Israel has proven that there are may effective ways to control a border, if only there's the will to do so.
I have fewer doubts about what Cruz will do, vis-a-vis conservative positions and principles, than Donald Trump. Trump to me is a high rolling, Casino shiester who'll do anything that pleases trump. Trump first and foremost, is for Trump, and everything in his past history has supported that thesis.
I think that Rubio, Bush, and Carsen are all more reliable conservatives than Trump. Then again, the campaign B.S. flying between these camps is leading me to doubt all three of them, but we're not going to find a perfect man. (Regrettably, Jesus Christ hasn't registered for this election, but I have it on good authority that He'll be back here soon!)
If I'm wrong, if Trump wins and becomes the next "Ronald Reagan (or better), I'll be pleasantly surprised. However, logic and evidence doesn't take me there.
FReegards.