If the wires going to the main panel connect to dedicated breakers, a 2-pole ( a single 2-pole breaker), two single-pole ganged (1-wire to each breaker), then the voltage is 240. Please measure, using a voltmeter,between the 2 wires.
I will add that the 3.4 kW at 240 VAC, given the 120/240 choice, means that the current draw will be 3.4 kW = 240 VAC x XX Amps,,, or XX Amps = 14.17 A. This assumes the power factor = 1 (electric resistance loads, instead of motors, which for an oven is true).
Power = VI (x power factor which = 1 for electric resistance heaters), or votage multiplied by current = 240 x 14.17 = 3.4 kW, the name plate rating. That means that when the oven is fully loaded, all burners on, oven on, etc, this is what the manufacturer claims the MAXIMUM power draw will be. It will usually be less than this because all burners will not be on at the same time and the oven may not be used with the top burners.
The main panel breaker will reflect the maximum power draw for this appliance. The diversity (all breaker loads will never be active at the same time) of all the applicances in the home means that the main panel does not need to add up to the sum of the breakers installed.