How to send ADC results over USB to my PC
Simplest is to make USB to virtual serial port (USB VCP), you have a library for that as well the example and drivers for windows. Once you plug it, you will see a serial port at your PC. Then in mcu program you can send it in orther you want with print function.
If you are familiar with Matlab then you can use STM32-MAT/TARGET and have possibility to use STM32 with Matlab/Simulink.

PS: 2-3Mbit that would be a little difficult with this approach. But do you really can process such stream of data at the PC side?