The 'Application Guide' categorizes pay-stubs/salary slips as 'Additional Supporting Documents'
In my case, I had to provide copies of my pay stubs and also my appointment letters as my reference letters did not specify the 'annual salary plus benefits' the organizations I worked for provided me with.
I guess you do not have to submit your salary slips, but it wouldn't hurt to go overboard and send them along with your other documents. Like others suggested here, it is better to have the original pay slips, just in case. And it would be even more of a pain if Ontario were to ask you for salary slips later during the process and you don't have them handy!