First point: I wouldn't recommend a 555 in any case, I've seen the maximum frequency given as between 500kHz and 2MHz (depending on the particular type) but getting it to work reliably at those frequencies is not going to be easy and to get a 50:50 duty cyle square wave would be particulalry challenging.
On the bigger question, the problem with doing it this way is that you have to adjust the filter to exactly the same frequency as the oscillator, so it usually easier (although not easy) to make an adjustable sine wave oscillator in the first place - given that a sine wave oscillator is just a filter with a lot of feedback! However if you get hold of circuit diagrams of analogue oscillators which do this you will see that they are still pretty complex, in particular keeping the level constant over the frequency range and temperature is very difficult. So, what would normally be done now is to digitally generate the sine wave. Whilst I have done this in the past I'm by no means an expert, but a web search on Direct Digital Synthesis (DDS) will find a lot of information.
Best place to look for examples of simple circuits are amateur radio websites, search for Variable Frequency Oscillator (VFO).
Andy Millar CEng MIET CMgr MCMIhttp://www.linkedin.com/in/millarandy
"The aim of argument, or of discussion, should not be victory, but progress." Joseph Joubert