Hello,
If you are sponsoring her visit, prepare an affidavit , attested by lawyer . This is an oath explaining your full name , address , status in Canada, employment information ,role, how much you make and the oat statement includes the details of your responsibility during her stay in Canada. Before, i submitted an affidavit like this notarized by a lawyer.Some say, you don't need it notarized. Uploading documents is at the end of the application system. It will have mandatory and optional sections. If they didnt give a button to upload the affidavit,you can add it to the invitation letter as one PDF and upload it.
Make sure, you attach past 3 years CRA assessments, you past 6 mont pay stubs, your investments and past 6 months bank account statements(which i got the print from bank and have them stamped).
If your spouse is employed ,it will be much stronger if you add her as a sponsor and attach the same documents. you can attach proof of funds as one pdf under optional documents category.
Hope this helps.Good Luck