Since you're using all extract, I would probably go with a wheat beer base. Cream ale would require mashing some flaked corn.
Just pick up enough wheat extract, which is really a combination of wheat and 2-row malt extract. Lightly hopped (15-20 IBUs probably - maybe even less, but I would hesitate to go that low) and, like mentioned above, add blueberries and a vanilla bean to secondary after fermentation is complete.
I'd go with 0.5-1 lb of blueberries per gallon.