Betting on two big favourites without knowing anything would, in my opinion, be a mistake. Actually betting on such favourites would probably almost always be a mistake as they are usually overvalued because the public does not like to bet on big dogs. And parlaying doesn't mean anything EV-wise.
However, since I'm advocating against betting this it would probably be wise to bet as both teams will win, and be it only to prove me wrong. ;-)