If you're going to trade the car into a dealership (regardless of brand), you're going to take a big hit financially. Dealerships often make more money selling used cars than new cars because a high-demand used car is difficult for consumers to find, so the dealership can sell it for a high price without competing against other dealerships. The dealership wants as much profit as possible (of course), so their objective is to give you as little as possible on trade, and then flip the car for as much as possible.
When I was buying my Impreza, I gave the Subaru dealership the opportunity to take my pristine 2010 Golf TDI in trade. They offered $16.5k, and wouldn't go any higher. I sold the TDI myself for $22k.
So if you don't want to take a financial beating, you're going to have to sell the Impreza yourself. Trading it in will cost you dearly. As Zeeper said, the Impreza is a desirable car, so it will be easy for you to sell it for much more than you'll get in trade (especially living in a cold-weather climate like MA).