Yes. If visiting your friend is an important enough element of the reason for your proposed trip to mention it in your application, you should provide an invitation from them to support the stated intention. If however it’s just a vague plan to ‘drop by’ at some point during your trip it’s not necessary, IMHO. The basis on which an invitation letter is usually necessary for most visitor/tourist visa applications is explained in the answer to your previous question Is Invitation needed for Schengen visas?
Based on your previous question Canada Visa Rejection, needing Advice on Documentation you have been refused a Canadian TRV under Paragraph 179(b) of the IRPR, which is a section of Canada's Immigration and Refugee Protection Regulations that allows visa officers to reject applications on the suspicion the applicant might try to stay in Canada beyond their temporary stay. Unfortunately, as you’ll probably be aware, Nigeria is universally seen as a high immigration risk country. Making a fresh application where the only change in your circumstances is mention of visiting a family friend in Canada won’t remove that suspicion, with or without a letter of invitation.