I have a 2000 cavalier with a 2.2 ohv manual tranny and was wonering if an ecotec or a 2.4 will bolt up in its place

Either will bolt right in place since they both came in a J-body. However, your current transmission WILL NOT bolt to any other motor but the 2.2 OHV and GM's V6 motors ( 3100, 3400, 3800)

So if you want to swap to a 2.2 Ecotec of the 2.4L you need a transmission that was originally mated to that motor, and wiring harness and PCM.