Ok, I had the same situation where I was issued a visa but no letter of introduction received. I read countless threads where people were asking the same question, but unfortunately, nobody bothered to post what happened after. And then, there are those who would invent things like the letter is not required anymore.
I applied for TRV and work permit. and got the passport back 1 week before the travel date. No letter of introduction received. I emailed the CIC, and was told that I should expect an answer in 28 days, working days! - thanks ...
I took my chances and landed without the letter, trusting those who would tell you that the letter isn't important. Well, it is important. Without it, the officer could not print my work permit. Because if you do not have the letter, it means that some CIC employee did not click a button to move your application to a certain status. The officers will then decide whether they could admit you to Canada as a tourist, reminding you that you could not work.
So I ended up in Canada, without a work permit, despite having a job offer. Wandered around for a week, before CIC realized their mistake, and sent the letter. But this is not enough. You cannot take the letter and show up somewhere. You have to leave the country and reenter.
Two thumbs up!