"Bu seçimi yeni bir parti kazanacak."

In my opinion, the meaning is the same and they are interchangeable in life. But on Duo, in terms of grammar and direct translation, your sentence uses passive voice, while Duo's uses active. So the subject of the sentence switches and the verb would take a different form in both languages:

• will win = kazanacak (active)
• will be won = kazanılacak (passive)

Active ("kazanacak")- The new party (subject of the sentence) will win this election. (The party will actively work to win.)

Passive ("kazanılacak")- This election (subject) will be won by the new party. (To be won, the election doesn't have to anything but exist.) More information on Turkish passive voice available HERE :-)