Hot tub 120 havc 20 amp what size wire and breaker do I need to hook it up

Is it going to be direct wire or will it have a plug with an integral GFCI?

I was going to hook it to a gfi breaker.. so it will be direct plug, but should I use a 20 amp breaker

Since you no doubt have a motor in the pump, you need, by code, to rerate the load at 125%. Therefore, your load is 25Amps. I would use a #10 Cu wire and a 30Amp breaker.

What do the instructions require for electric service?

Spas are typically rated by the size of the circuit they require. As such, you needs a 20a GFCI and 12 gauge wire.

MA0641 is correct about the 125% rule, HOWEVER, your pump motor probably is rated at a MAXIMUM of 12 amps (and more likely 8 to 10 amps). As such, a 30a circuit isn't necessary (125% of 12a is only 15 amps).

Unfortunately, he never answered as to what the plate says. I interpreted "hot tub 120 havc 20 amp" to mean it was rated at 20 Amps. Why ask what size breaker if he has a 20? It could also have a heater.

It almost certainly does have a heater... but the way these things are designed, only the low speed of the pump (generally around 2 to 3 amps) runs when it's heating. When you turn on the high speed of the pump, the heater shuts off... The is the industry standard for how they operate.