You can find all of your answers using ohms law, a 30 amp breaker is a bit overkill allow me to explain: Assuming your supply voltage is 240 volt AC you calculate as follows. 2000watts devided by 240 volt =8.3 amps. Table 2 of the CEC(canadian electrical code) shows that 12 awg NMD copper is rated for 20 amp more then enough. 20 amp breaker recomended that will allow room to add to the circuit later if needed. Up to 3750 watts of heat. EX: 3750 watts devided by 240 volts =15.62 amps thats the recomended 80% circuit loading of the CEC 20 amp times .8 =16 amp

It's enough to power the heater, no problem. But the breaker current is determined by the section of the wire that's protected by it. The thicker the wire, the higher the breaker's rating can be, but you can't have a 30 amp breaker with thin wire behind it. I don't know the figures by heart, but you should certainly find this on the Internet.