Shigeru Miyamoto has stated that Yoshi WILL be in Super Mario Sunshine, but he said nothing about Mario being able to ride him...
As for Luigi being in Mario Sunshine, highly doubtful... The reason is Luigi already had his own solo role in Luigi's Mansion, and the odds of him appearing in his second game (even as a partner for Mario) are unlikely. We have seen no references to him in Mario Sunshine yet (same with Mario 64)...so don't count on Luigi being in the game (at least as a playable character).
And yes, Mario Sunshine does look remarkably similar to Mario 64 (aside from Mario's water tank), and this is because Shigeru Miyamoto said that this is the "true sequel to Mario 64"... so obviously they had to make it similar in terms of gameplay and graphics. Also, Super Mario Sunshine is still early in development, and that's the reason why it looks so grainy when compared to Mario 64. The GameCube is capable of producing some of the best graphics ever in videogames (think: Smash Bros. Melee, Pikmin, Star Wars-Rouge Leader), so count on Super Mario Sunshine to have some of the most detailed features ever put in the Mario universe! We've already seen the extreme details of Mario in Super Smash Bros. and even in the early screenshots of Mario Sunshine, it seems that Nintendo is pushing the graphics of Mario Sunshine even further with the facial expressions on Mario's face and the detailed textures in his clothing...
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"Bwa ha ha! Guess who it is, loyal Mario fans...
It is I, King Bowser... ruler of all Koopas, big and small. I have come to take over the Mushroom Kingdom (no, not the place...I mean the WEB SITE!)! Deezer, you will surrender your troops to me, or else you will never see your precious Mario again! Bwa ha ha ha ha ha ha ha ha ha!"
Edited by - Mario Maniac on 4/25/2002 6:17:41 AM