Depends on when in March. In very late March, cherry blossom season will be starting in Kyoto, Osaka, Kanazawa and probably Tokyo. In early March, you should look further south such as Fukuoka, Nagasaki or maybe Hiroshima.

Having said that, if this is your first, and possibly only, visit to Japan, I urge you to consider Tokyo and Kyoto. Kyoto and nearby Nara will give a glimpse of older, historic Japan that no longer exists and Tokyo is the epitome of ultra-modern, high energy, "happening" Japan.