Letters may not help but its sad to say it does help who you know. My wife was refused a trv, understandably so as she had a PR file in place to come live here so that worked against us, but we wanted to be together for the time that was going on. Luckily we had contacts in the gov't, I'm talking Trudeau level contacts (not an exaggeration). I personally went with this contact to see a MP and the MP in front of me called Ottawa, basically said we need to get this trv done they are vouching for it. This happened via speaker phone while I was there. Wife was approved for a three week visa, she came saw what Canada was all about, and left before her time was up following all the rules. I had to keep in touch with the MP's assistant throughout to let them know about my wife's whereabouts, I sent photos of her boarding passes and stamp on her passport when she arrived back in India as proof that she left. MP said this is bs, that they see so many refusals for genuine travelers from south Asian countries that a lot of their time is spent dealing with such issues vs other issues in the community.
Two months after that I applied again, this time I stated your previous concern was that she would not follow the conditions of her visa and she has proven to follow the rules etc etc ....was approved within 7 days from India for multi entry trv. Wife was given 6 months at entry luckily our pr came through month 5 so she didn't have to extend her stay or go back.