Yes, it can. Fill it into a freezer bag (squeeze out all air in the bag and seal it well) or a covered container before freezing. To use the filling, thaw and bring it to room temperature. Heat it up slightly if required or if the filling is no longer thick as the cornstarch has a tendency to loose its starchy effect after freezing. If the sauce does not thicken, you can try adding some more cornstarch slurry (cornstarch mixed with water) and cook it until it thickens. If you intend to keep your blueberry filling for more than one week, I would recommend it to be frozen.