My employer is not willing to provide me with a reference letter with roles and responsibilities, instead they will only provide a standard letter with my designation. So I am planning to obtain a reference letter from one of my colleagues(a senior) and get it notarized. Also I will submit an affidavit stating the reasons for me submitting the reference letter from colleague instead of the company reference letter, with all other necessary documents like offer letter, joining letter, pay slips etc.
Will CIC consider this as MISREPRESENTATION?
In reference to the discussion about whether or not your colleague's letter should or shouldn't be on letterhead, (and speaking as an HR Professional), your letter from the senior colleague should NOT be on letterhead even if he/she has access to it. HR represents the Company, so if they refused to give you the letter in the requested format, your senior colleague cannot then go ahead and do it on letterhead himself - any letter in the requested format that he writes for you will be written in his own capacity, not as a representative of the Company (since HR already refused to allow this), so it can't be on letterhead. His letter needs to be on plain paper, and should be otherwise endorsed in some way (notarized preferably, as you mentioned).
However, I would upload BOTH the letter from HR on letterhead (even though it will be lacking roles and responsibilities) AND the notarized letter from your senior colleague, as well as evidence that your colleague works at the company (copy of business card, copy of employee ID, etc.) - these documents together should be strong enough for your application, although if you still want to include your offer letter, joining letter and pay slips, you can add those as well.