Yes.
You have to race (& win) the single race series' in the arcade mode.
You also need to do this to reach 100%. If ou just want to unlock the tracks, do it on easy. If you want % ponts towards 100, do them on had, and you won't have to do the easy or medium.
AO
Actually to add to that:
First: Welcome to the forum
Second: If you check the "Look here before you ask" at the top of the main forum, you'll find a link to the Arcade FAQ.