The anti-aliasing filter could be a passive RC filter or an active filter depending upon the noise level outside the signal bandwidth and the A/D conversion speed.
The "gain multiplier", which I assume means simply a gain stage, can be performed by an opamp amplifier circuit depending upon what the input voltage level is and how much gain you need.
There are zillions of A/D converters out there, built by TI, Linear Technology, Analog Devices, etc. You need to decide on the conversion speed (at least twice the highest input frequency of interest) and the accuracy (number of bits) required.
The µC selection will depend upon what you want to do with the A/D signal, of course.
So your first step is to put requirement values in each of boxes. You can't do the design without specific requirements.