Traditional animation and the game voice actors - except Bowser: the little clips of M&L:BIS and other such games don't sound like they'd translate well to full dialogue, and SMS's voice was terrible; my choice is and always will be Christopher Heyerdahl (example). It would be a retelling of how the bros come to the Mushroom Kingdom and save Peach for the first time, while the events of Yoshi's Island and Donkey Kong are flashbacked/discussed, with Kamek as the secondary antagonist and even Pauline appearing (to up the girl content). Peach would also be more than a useless damsel in distress love interest, with the emotional heft actually centering around Mario and Luigi's (twin) brother relationship.