Raj2014 said:
Yes Invitation Letter is must when you apply for visitor. Student in Canada can invite you too.
Nothing like only PR can invite you.
That is only half the truth. Of course, a non-PR can INVITE someone. But if with inviting, you mean sponsoring/guaranteeing the visitors economic stability, while in Canada, then only a PR or citizen can do it. You declaration of support will count for nothing, in the review of the application.
So it depends on, if you are able to support yourself. Your friends income or economic situation won't matter, because he is only granted temporary residence in Canada.