I think Brosseau makes it. I don't know if he is one of the 13 best position players, but I do think his skill set complements the rest of the roster enough where he is part of the best 13-player group. I think Turang and Miller are your opening day middle infield in Nashville. That leaves Toro, Naquin, Hiura, Frelick and Voit battling for two spots.
You know how everyone has spent the offseason talking about how awkward a fit Keston Hiura is for this roster? The same goes for Luke Voit, except at least Hiura could be a break glass in case of emergency option at second (hope you'd never have to use it, but at least he has experience there). Both seem like protection in case Winker hits a setback physically.
I'd like to see Frelick take one of the last two spots, but I am increasingly thinking it isn't going to happen. Personally of the remaining ones then, Toro and Naquin seem to best balance the roster, so I'll go with them. I don't blame anyone for inserting Hiura or Voit, though. Having both of them in camp sure makes it look like the Brewers think that profile has a place on this roster.
As for the bullpen, it depends upon 1. health and 2. how many of the out-of-options (or rule 5) guys pitch themselves out of contention by opening day. @Brewcrew82's bullpen picks look like the best April bullpen, but it wouldn't shock me if Strzelecki or Cousins starts in triple-A. If either Varland flashes upside or Wilson looks better out of the bullpen than as a starter, they could keep them and send one of the pair with options down. Injury or ineffectiveness would likely have whichever one is sent down on the roster by mid-May anyways.
I'll guess that scenario plays out and Strzelecki is swapped for Varland.