I'm not sure if there is any specific format... or a thread where someone made a format.. I just wrote it the way I would usually write a business letter... for exp in your case:
To: Citizenship and Immigration Canada
Dear Sir/Madam,
In order to prove my relationship with my relative in Canada (my maternal uncle), please find attached the following documents:
1 - My birth certificate, showing my mother's name (mention her name here)
2 - My mother's marriage certificate, proving her father's name (mention your grandfather's name here).
3 - My uncle's birth certificate, also mentioning his father's name, therefore proving that my mother and MR. (uncle's name) are real siblings.
Please note that, due to the fact that there was no requirement to issue Birth certificate in Pakistan during the time of my mother's birth, my mother does not have this document. As a result, the only proof of father's name that is available is in the form of her marriage certificate. Therefore, I kindly request that you consider this legal document as proof of relationship.
Something like that should be enough.. and then you can sign it...
Others may be able to advise further... but this is what I would do..
You had mentioned that the score is 440... is your IELTS maximum? I would suggest to wait for next ITA, and if scores are still not going below 450 (there is 50-50 chance that it may go down), then maybe you can redo IELTS to make sure it is above 450...
