I think this would change how Russia's cav works too much. All of their cav units would essentially be made into Heavy cav, at the detriment of Hussars/Lancers.
Instead, the Bears should be given to the Partizani, who realistically should have at least had one bear wrestled into servitude by the age of 11, living in the cold bleak of the bear-infested Russian wilderness.
Russian wilderness can only be tamed by russian peasants. Also Bear cavalry can be balanced by adding Swedish Moose Riders
