Open/close low voltage AC circuit with 3.3 VDC signal
You could do this, however you should use the non-zero crossing type of optocoupler. The zero crossing type have an inhibit voltage that can be as high  as 20V. One type would be the MOC3023. 

Be aware that the triac will drop a volt or two so you won't get all the voltage on your load. You don't mention the current or other load characteristics so I can't comment further on what might be a better solution, though if the current is low (such as 500mA) you should consider an opto-MOS SSR. 

You can reduce the resistor to pin 6 to 51 ohms and leave the rest. The snubber (39 ohms/10nF) is optional particularly if you have a high voltage triac and a benign load. Use a relatively sensitive gate triac (quadrants I and III only are important). A 20mA gate trigger will cause you to lose ~1V at the beginning of each cycle as well as the conduction voltage drop. That's not much power because the maximum dv/dt of a sine wave is where it crosses zero, but it can cause EMI and may affect some loads. 

Sometimes other trigger circuits are used such as "picket fence" pulse triggering through a pulse transformer or a DC-DC converter driving the gate and providing isolation. 

The opto-MOS type of switch behaves more like a low value resistor when it is on.