20man: Let's break down where all three are at right now heading into OTAs in the coming weeks and then training camp in July:
Giovanni Manu was certainly a project in Year 1 transitioning from the University of British Columbia to the NFL. There was a lot that was new to him — mostly just adjusting to the speed at this level and technique needed to counter it, which is no easy task when it's all new. The Lions are going to try him out at guard some, according to Campbell this offseason, to see if it's a fit. I'd also expect him to compete with Dan Skipper for the swing tackle role. The move to guard will be interesting to watch. His size and athleticism are intriguing there.
For defensive tackle Brodric Martin, it might be his last chance to crack the roster going into his third season. I thought he was making some progress in camp before an injury set him back last year. Can he consistently play with good pad level and put himself into the defensive tackle rotation? It will be tough with the return of McNeill, Reader, Onwuzurike, Mekhi Wingo, Myles Adams and with the recent additions of Williams (draft) and Lopez (free agency). This could be his last chance to prove he can.
Running back Sione Vaki made an immediate impact on special teams and I see him having a similarly big role on teams in all four phases this season. Can he supplant Craig Reynolds as running back No. 3? He'd have to prove that in training camp and the preseason, but his role on teams will be key for the Lions all year.