As Khris implied, it's a case-to-case basis. Whatever worked for your step-brother may not necessarily work for you. There may be differences in age, circumstances, etc. that the visa officer considered as a whole.
The documents that we gave:
Letter of Employment
Invitation Letter
3months bankstatements of my husband
3months payslip for both of us
Affidavits
Flight tickets that we booked
Letter of my fathers work
Do you have any other assets aside from your bank accounts? Properties, land, car, etc.? How did you submit? Online or by paper?
Even if you are staying with your dad, you have to show enough money to support your trip as if you are not staying with him.
Affidavits and booked tickets are useless. This may work for visas for other countries, but not Canada.