The official Japanese Sonic Free Riders website has received a makeover today, along with new updates that include the above new trailer and some new screenshots. In the screens and trailer we see more of Dolphin Resort and Rocky Ridge played in both single player and co-op modes, in which one mode sees you synchronized with another player. The trailer also acts as a tutorial to show you how the game is controlled, including the stage specific elements such as swimming, steering a minecart and riding a newly revealed bobsleigh. It looks like there is plenty of physical interaction involved in the game to keep players fit.
Thanks to Woun at the SSMB for the heads-up!