A sponsored spouse is barred from sponsoring a new spouse for 5 years after getting their PR. If they want to sponsor a parent, they need to show that they meet the minimum income requirements for the past 3 years so they need 3 years of tax returns in Canada to prove that. If their sponsor co-signs the application and the sponsor meets the income requirements for the past 3 years, then they would not have to wait. Sponsoring parents was taking up to several years before immigration temporarily closed the program. They have now re-opened it with more requirements.
If you want to sponsor your parents for a visit visa, you do not have to show income for 3 years. If you try for a super visa, you have to show that you have enough income now. If you try for a regular visit visa, you don't really have to show income at all but it would strengthen the application if you do.
