The
Hohenzollern Archbishop of Riga, then ruling a fairly large chunk of what was known as Livonia, wanted to secularize his bishopric into a Lutheran duchy. He failed OTL, but perhaps circumstances could lead to his success, perhaps his line could eventually die out and perhaps the inheritance could fall to the Brandenburg Hohenzollerns? If you add a lucky Courland inheritance on top of that, you'd have most of Livonia in Hohenzollern hands.
That's a bit of a stretch though. With Sweden and Russia's Baltic ambitions, and Poland-Lithuania already in the neighbourhood, it's hard to imagine that anyone would let the Hohenzollerns accumulate a Baltic empire like that, and they wouldn't exactly be in a position to effectively defend their holdings either.