You would really need to know when they arrived in USA,
and have some clues as to where they first lived. I did have another look for them, and there was a William Pollock and a John Pollock arrived at Passamaquoddy, Maine - but they arrived 15 years apart from one another, so there is no way of knowing if they were definitely brothers.
Besides, aren't you looking for Pollocks who arrived further south?
Anyway, John Pollock, born abt 1817, arrived at Passamaquoddy, Maine 1834.
And William Pollock, aged 34 born abt 1815, arrived Passamaquoddy, Maine 1849.
When you look at their dates of birth, it does makes you wonder if they could be brothers. But, as you seem to be looking at ships arriving further south, I doubt if they are your ancestors.