Switching between two sine waves using analog circuitry
Why don't you use one wien bridge oscillator and use "analogue" switches to alter the resistor values in the oscillator. At least this way the changeover from one frequency to another is self-synchronizing and possibly won't "glitch" the speaker as it might if you used two wien oscillators.

If you do decide to use two oscillators then use analogue switches for selecting one output or the other.