Writing a letter of Explanation Canada, Please Advise on Missing information

Your point should be to address the issues raised in the previous rejection, and to give all the information they need which addresses their concerns.

Their concerns are that they think you will not leave Canada at the end of your planned stay. You must convince them otherwise by establishing strong ties to your home country (a permanent job with a decent revenue -- by Canadian standards, not Nigerian ones). You should on the other hand probably not drown them in a lot of unnecessary documents and verbiage.

Instead of giving lots of bits and pieces of information about everything and their cousin, make sure you have complete and exhaustive information and supporting documents on the points that actually count.

As it stands, the information you give looks quite confusing and can be perceived as bit contradictory. You state you have a full time job, plus a part time remote job, plus a job managing your family's business. This is clearly confusing.

Also, you are mixing business and personal accounts and revenue. This is a common mistake, but the officer handling your application does not care about the revenue of any company you own, manage, or work for. They care about your revenue.

For your full-time job, you should:

• Provide evidence of that job (your work contract, and at least your last 3 payslips).
• Provide at least your last 3 bank account statements.
• Make sure your salary correctly shows up on your bank account statements and the amounts match.

For your part-time job, what is your status? Are you self-employed? Running a company? Salaried? You should provide associated relevant information. Correctly separate any business income and statements from your own actual income and statements. In many cases, you should not even provide any business income or statements, though this may vary.

For your job managing your family's company, the same applies. Are you salaried of that company? If so, provide work contract, pay slips, and bank account statements which show those payments. If not, the income and statements of the company are probably not very relevant.

Prefer having (simple, concise) tabular information rather than long text. Which do you think is clearer? You long and convoluted explanation:

My salary monthly (from my full-time job is about 450,000 before tax and 427,500 after tax monthly in Nigerian Nairas, and 5,130,000 nairas, after tax annually) and my part-time job I make about 350,000 naira from my remote job monthly where I work as a Mobile applications Developer. Altogether I make 777,000 (Seven hundred and seventy seven thousand Nigerian nairas) which is about 2,777.85 Canadian dollars monthly and 33,334.20 Canadian dollars annually.

(and that's only a small part of it)

Or:

Job                          | Monthly Salary (NGN) | Monthly Salary (CAD)
-----------------------------+----------------------+---------------------
Software Engineer @ XYZ Bank |          450 000 NGN |            ±1600 CAD
App Developer @ Foobar Co.   |          350 000 NGN |            ±1250 CAD
-----------------------------+----------------------+---------------------
Total                        |          800 000 NGN |            ±2850 CAD

(I have no idea why in one case you have figures before and after tax and in the other only one figure).

Your situation is complex enough that it probably warrants using the services of a good, honest lawyer (not some agency that will pretend to do the right thing and file bogus info). Remember that you remain solely responsible for anything that is filed in your name, so do not let anyone submit documents which do not represent the truth.