I would bet more that Brady doesn't start this game than that the Pats would lose it. Brady won't start - and the Pats are going to lose. The Steelers aren't a bunch of fluffs and Bellichick is great, but he doesn't throw the ball last time I checked. He also doesn't defend against the pass.
The Patriots will be relying on an improved front seven hopefully a healthy Dominique Easley, First round One Tech Malcom Brown, with Collins, Ninkovich, Mayo, Hightower, and Chandler Jones along with high ceiling free agent acquisition Jabaal Sheard.
The front seven is going to be really good, but Bradley Fletcher, Malcolm Butler and Logan Ryan are not a very good pass D, and won't be fully gelled in week one. It's not like they're facing nobodies out there in Antonio Brown, Martavis Bryant, and Sammie Coates (I like Wheaton out of the slot, but I can't help but think he gets bumped by Coates who is fantastic.)
Sure, the Steelers aren't going to be able to run the ball incredibly well without Leveon Bell, but they've certainly found their identity in slinging it, and their O Line has really gelled now that DeCastro has spent some time healthy. Besides DeCastro, Pouncey is one of the best Centers in the league this side of Travis Frederick.
In the end, we can talk about Labeau, we can talk about Polamalu (I mean, come on, it's not 2008 anymore), but I'll tell you what- I think by the third quarter we will see Garapollo making Senquez Golson and William happy look like superstars.
I see the Steelers jumping out to a lead, I see the Patriots having to keep throwing to get back into it. I see Garoppollo making good plays, but I also see him making more mistakes than Roethlisberger. I see the Pats having to send a bunch of blitzes with their backs against a 10-14 point lead, which will lead to more man to man coverage on the backend, which usually opens up the vertical game which leads to more quick scoring.
That is a good reason why this game will go Over and will be won by the Steelers. I would say something like 37-24.