You cannot create ionic2 using ionic3 cli
Reason
ionic1 was on angular1x
but angular 2 was not updated version of angular1x but new rewritten for angular and hence ionic updated them self to ionic2 which used angular2
now the angular4 was released it was not rewritten of angular2, it was updated version of angular2.Hence ionic3 was updated and now used angular4.
it means even if you have ionic2 project but you have ionic3 cli installed , yet you can run and compile without any problem.
conclusion. ionic1 is different and ionic2 == ionic3 + some new features such as lazy loading.
Thr is no such need to create ionic2 project
but if you familiar with angular1x and not angular2 you can create ionic1 project with ionic3 cli