Yes I believe Bernie Sanders will challenge big banks if he is elected president. After the economic crash that took place in 2008, that problems with the United States' banking system became evident. Bernie Sanders has realized this, and has already gone as far as to file bills to break up the biggest banks in our nation. One example would be legislation he introduced in May of 2015 as an attempt to do exactly that.
Whether or not Bernie Sanders is able to effect real change, which seems highly unlikely given the obnoxious obstinance of the Republican members of the senate, he will take the challenge. Every speech, every radio address, every article that Mr. Sanders has written over the course of his career in public service, he harkens back to changing the income inequality equation.
While I do believe that Bernie Sanders would want to challenge banks if elected president, I do not believe that it would be logistically possible. With our bi-partisan government system, I do not believe Bernie Sanders would have the support of the other branches of government to successfully challenge these entities.
No, Bernie Sanders will not challenge banks that are "too big to fail" if he is elected president. There are a number of other issues that Bernie Sanders can tackle if he becomes president. Banks that are "too big to fail" may not be considered enough of a significant issue for the president to address.