Hello there,
I agree with the PWM suggestions but if you are going to generate PWM using an analog method then you probably are seeking to generate first a sine wave reference, then use a triangle wave compared with that sine wave to generate the PWM pulse widths. That gives you the proper pulse widths to drive the H bridge with. That's not my preferred way to do it, but if you are stuck in analog land then you may have less options that work as well as that one.
To this end, it is easier to generate a sine wave with a sine wave oscillator. There are different kinds out there so you should look around and see if you can find one you like. You can get some very clean sines out of these things and at line frequencies it works pretty well even with cheap parts. If you intend to change frequency you'll have to give it some more thought.