The flow of electric current occurs because we have a high potential of electrons gathered at the positive terminal and a low potential of electrons at the negative terminal.  It doesn't have so much to do with the charge associated with each one as it does with the fact you have an inequality between amounts of electrons available.  When you complete the circuit by turning on the switch, the electrons flow naturally from the high potential to the low potential, which is from the positive pole to the negative pole.  Think of it this way:  if you have a stream of water, and you build a dam to hold back the water, you get a buildup, a reserve of water behind the dam.  When you open the floodgate of the dam, you start a "flow" of water from the excess water you have available.  This water quite readily flows to the lower levels in front of the dam, where the water levels are low.  It is the same with the flow of electric current through a circuit.