You can play it by ear and see how your game is going and decide on Sunday. If you need huge upside and it looks like Allison is starting go with him. If you need a higher floor go with the safer Cohen.
I would go with Cohen. Not that he will go off like he did in week 4 again, but he is seeing more playing time and is a threat to score from anywhere on the field. Breida has been so good when healthy, but not sure that will ever happen this year. He is like an egg shell.