Can you use 4 ton furnace with a 3 ton condenser

Sure but your only going to have 3 tons of cooling. You can always go a little larger on the blower side but not the revers the condenser can not be larger than the air handler.

In some cases a 4 ton blower setup in the furnace might need to be droped a speed. Too much speed across the A/C coil in the furnace and you will not get the proper dehumidifing from the A/C. Also too much speed on the blower can also cause atomization of the condensate water and blow the water into the duct and not down the drain.