When is the best time to see the fall colours in northeast Japan?
What's the peak season for the autumn leaves in the Tohoku area?
この場合、次のような言い方ができますよ。
ーWhen is the best time to see the fall colours in northeast Japan?
「日本の東北の紅葉の見頃はいつですか？」
When is the best time to ...? を使った聞き方。
ーWhat's the peak season for the autumn leaves in the Tohoku area?
「東北地方の紅葉のピークはいつですか？」
What's the peak season for ...? を使った聞き方。
ご参考まで！
カナダ 
