Will an imported ME3 Shepard be the same as a new Shepard story-wise?

If I'm reading the question correctly, you're specifically asking about the New Game+ option of importing a Mass Effect 3 Shepard that has already completed the game to start over, is that correct?

If so, the answer is that it's the same as when you started the first time. If you started with an ME2 Shepard, imported it into ME3, beat the game, and then imported that ME3 completed Shepard to start over, the game still remembers all of the choices you made in ME1 and 2 and reflects those choices. There is no difference.

The benefit of importing an ME3 Shepard is his level, as well as all of your accumulated Armor, Weapons, Mods, Bonus Powers, Credits, Upgrades, and Intel Bonuses. Additionally, Weapons and Mods can be upgraded to a maximum level of 10 in a New Game+, versus a maximum rank of 5 in a standard game.