I don't think that the Bronco Sport is really comparable to the Forester - except in the broadest sense of them both being SUVs.
Will the Bronco Sport have a superior 4 Wheel Drive setup? Sure. But is it a full time system or a part time system?
The base motor (the small 1.5-liter turbo) has power ratings just about the same as the Forester 2.5 motor. Bronco is 181 HP, 190 lb/ft torque. Forester is 182 hp, 176 lb/ft torque. Note that the Bronco requires premium unleaded for the rated output. Not sure of the levels on regular unleaded.
MPG has yet to be determined for the Bronco Sport as yet. But in a similarly sized Escape, it's a bit lower than the Forester when equipped with AWD. Again, this is the 1.5 motor to the 2.5 motor and not for the Escape hybrid.
Bronco Sport - no manual transmission option. On the larger Bronco, there is a manual, but only on the base model. No other manual transmission offered.
Bronco Sport does have a bit more trailer tow - 2200 lbs... Major dimensions (length, width, height, wheelbase, track) are all within an inch or two. Forester is a bit bigger in most interior measurements, cargo space bigger in Forester with rear folded, Bronco a bit bigger behind rear seat. Many of the interior measurements are a wash.
Luckily, the 1.5 motor has been around for a while so you won't have to deal with too many teething pains of a new motor or transmission design.
But again, it's not a true apple to apple comparison - as the Bronco Sport is geared more towards the Jeep shopper (those that want a Wrangler ability in a more traditional SUV package. The Forester is geared more towards the "regular" SUV shopper - looking at the CRV, RAV4 and the Escape from Ford, as well as the more traditional Jeep Compass and others in that market segment.
As we don't yet know what the Wilderness Package is going to be (just a looks package or a more off-road oriented Forester?) there's no way to compare it...
And seriously, the typical Forester shopper will not be a Bronco Sport shopper.