AFAIK since its under 6 months you still need to qualify for a standard TRV which means you need to show strong ties to your home country and that you will leave when its over.
This letter is good but what else do you have that ties you to your home country.
Job?
Family?
Home?
In essence and be honest with yourself, what ties do you have that after 4 months you will leave and not try to find a job? Thats what the VO will ask and that is what documents you need to show.
In addition you need proof of finds that you can afford 4 months in Canada without working
And you should show a strong travel history.