You only got your premium seats because LH has lots of excess F capacity across the Atlantic from its US gateways so makes more than the normal number of award seats available. This is not the case for its Canadian gateway flights, nor for AC's own J. It is most unlikely you will find space in the front cabin other than the routing you now have. Though technically speaking you are not permitted to upgrade an award ticket from the class it was issued in, you might find a sympathetic UA agent who will put you into an empty F seat should one be available on the day of flight. Otherwise, grin and bear it, then enjoy the comforts of F ex-ORD.