I have used the PCA PWM to create 3-phase sinewave outputs ones; it's not that difficult, but the question if it is a usefull for you depends very much upon the max. frequency you want to establish. This is especially important if the glithces that might occur shouild be sufficiently suppressed.

The thing is that - obviously - a higher frequency for your PWM generation is desirable, so you would set your PCA clock to f(osc)/4 mode. If you would want to suppress glitches as much as possible, it is necessary to reload the PWM set-value at the very moment the PCA timer is 0 - the PWM outputs are all low. Catching that very moment may be quite awkward, if not impossible.

If the signal frequency you want to generate is low (e.g. 60Hz), you can add a quite large capacitance to the outputs (immediately behind your output driver, preferably a push-pull transistor configuration) that will work as a low-pass filter, effectively killing the effect of the glitches.

As for the software: you can create a simple look-up table that defines the sine-wave. It doesn't need to be that big (you only need a quarter wave) and use a timer to output the new PWM setvalues at regular intervals. Again, for low frequencies in combination with sufficiently large capacities, you don't have to bother about the glitches, so just reload. If you have an oscilloscope you can experiment with the size of the capacitors (much depends upon the load you put onto it, so make sure that you provide a steady, buffered output) to fine-tune the resulting waves to minimum distortion.

Have fun.