Advanced Battle featured them all, up to Gen III obviously. But after watching all the D/P ones on Youtube it seems that Sinnoh League Victors features the most legendary Pokemon, it's the last season in the D/P saga. So you were looking for the wrong thing. :P
No, thats not the one i dont think. i do recognise some scenes (the flyover by the Kanto birds, and the space bit with Mew and co), but the one i remember had others in like Celebi, the sinnoh lake trio, and shaymin in it, and didnt really feature many of the other, non-legendary pokemon seen. The one i saw certainly used these scenes, but added other legendaries to the mix. it wasnt a fan creation either.