Slice pound cake 1/2 - 3/4" thick. Cover the bottom of a 9x13" baking dish with slices.
Sprinkle agar over fruit juice in a pan and let soak for 15 minutes.
Slice 1 cup of strawberries. Simmer agar in juice until dissolved (about 10 minutes for flakes). Let sit until thick, then stir in sliced strawberries and 1 cup of blueberries. Pour over pound cake and let sit until juice is firm.
Whip cream until foamy, add sugar or honey and continue whipping until peaks form. Spread sweetened whipped cream gently over juice.
Place blueberries on top of whipped cream to form the blue field of the American flag. Cut remaining strawberries into halves or quarters (depending on size) and place on whipped cream to form stripes.