Bargnani will most likely start based on his performance against NJ in the final 2 games. He showed he can score, and played so pretty good defense on Carter and Jefferson. Rasho, I think though will start the beginning of the season, and Bargnani 20-25 games in. If Il Mago just improves his rebounding and post game, he should be a huge factor next season, which could be great for Bosh will get to score more and more.
Rasho is a solid starter, and Bargnani is a better energy player/scorer off the bench. Sort of like how Ginobli came off the bench.
I still think though, due to Bargnani's size, he will get the start. To compare Manu is different, because Manu chose not to start, he was asked, and said he rather come off the bench. Bargnani, IMO should start mid way though the season because he will get better and is going to be a 20 PPG 5 RPG kind of player.