Do I have to say Yes to "have you ever used any other name?" if I did?

Consider the two ways you can be wrong here: you can omit it when the right thing is to include it, or include it when the right thing is to omit it. One is much worse than the other.

If you include it when you should omit it, you believe (without evidence, you've just heard horror stories) that it might delay your application. ("I will have to provide explanation for name change, reason for name change and they could ask additional documents too. I've also heard from people that they keep applications on hold for months because of this as well." and "they put your application on hold and do very lengthy background checks and ask dozens of documents on previous name, and all this for nothing") This sounds bad. But it's just rumours. There isn't a spot on the form for "Why did you change it", and you don't have information on the web site that including this information will actually slow your application, nor what the "dozens" of documents are that you supposedly would be asked for. (I have not applied for a Canadian visa, because I'm Canadian, but I have applied for other visas, and included my former name (I changed my name when I married) and no country ever came back and asked for more details about when and why I changed my name. Just one data point, but possibly useful.)

If you omit it when you should include it and this is discovered, your application could be denied rather than delayed. Not only will you not be admitted to this country this time, for the rest of your life you will have to answer "yes" when asked if you've ever been denied entry to a country. (This tends to get you denied entry to whoever was asking. It certainly delays your applications.) Or if you get admitted this time, if the omission is discovered, you could be expelled or deported, with again permanent consequences for all the countries in the world you might want to visit.

Your question boils down to "should I lie on my form to speed up my application?" and I think you know the answer to that is No. Not just because lying is wrong, not just because you don't actually know that it will speed things up to omit your previous name, but because the consequences of being caught in this lie of omission will be enormous and you won't be able to fix them. You will just be someone who can't visit other countries. Don't risk that.

You may think you can get away with it because you didn't use the old name on visas etc, but you changed your name legally in your country and it's probably pretty trivial for the government to check if your current name and birth date are associated with a name change. The reason they ask about old names is because they may do a search on you, and they want to search using all your names. If they do a search and find your old name, you will (at best) trigger all the extra paperwork you wanted to avoid, or just be denied irreversibly for lying.

You should include your birth name in the application.

It may seem like an unnecessary complexity, but really it's just filling in one line of a form. On the other hand if you ever have to reveal that you in fact had a different name at birth (after having said you didn't) this will hugely increase the level of suspicion that you are not being open and honest with immigration. If you are unfortunate enough that some time in the future Canadian Immigration is looking for a reason to exclude you, having lied on an immigration form is enough reason for them to do so.

If you were named on your birth certificate, that is one name you officially used.
If you changed your name later, so you now have a different name on your passport, that is a different name so yes, you should mention your name from your birth certificate. At a later date you may need to use your birth certificate for something and if the name is not on your records they may assume you left out that name with bad intentions. (And that can lead to refused visa or even entry bans into the country.)

As a VWP traveler who is generally entering the US in transit to another country, I'm rather absent-minded at immigration, usually sleepy and jetlagged, just going through the motions. You don't have to give a lot of thought to what you're saying, because you just have to answer each question truthfully and move on.

Once, I was asked by the immigration officer if I had anything in my backpack that was bought in the origin country (where my flight had departed). I didn't remember. I knew exactly what I had in my backpack, which were a lot of personal computer accessories, but I certainly don't keep track of, say, where I bought a USB stick.

So of course that's what I said - "I don't remember". That has been the only weird experience at US immigration that I've ever had. The officer instantly changed his demeanor, and turned increasingly hostile (while still professional), asking the same question multiple times, telling me that he was in no rush and he could keep me at the airport all day if needed.

That woke me up. Sleepiness was gone, and as you say, I was afraid that I would have to go through unnecessary complications. But here's the thing: I was telling the truth, so I just kept on politely repeating the same answer.

After four or five times, as I didn't want to sound defiant by simply repeating the same answer again and again, I added something like "Officer, I'm sorry, I really don't remember. Perhaps we can move to a room, open my backpack, verify the contents and you can let me figure out what was bought where."

He smiled, stamped my passport and he welcomed me to the United States.

This doesn't seem an answer to your question, but it is:

So can I choose 'No' to avoid unnecessary complications?

You can't choose what to say in order to manipulate the outcome of the interview. You have to answer any question truthfully. When in doubt, be open! Provide all the information you have. It will be up to immigration to decide if it's relevant or not.

I told you about my episode because it shows that telling the truth, even when the answer isn't great, or it isn't what you think they want to hear, doesn't necessarily lead to unnecessary complications.

Conversely, as described or implied by all other answers, lying can and most likely will lead to unnecessary complications.

Do not lie to immigration, ever.

Well unless you're looking to be banned, of course.

Another example: you're entering a country that is asking you if you're carrying food, but you're not sure if what you're carrying is classified as food? Just say YES. Let the interviewer ask you and find out if what you have is acceptable. It's better to look stupid or naive or excessively compliant, rather than raise suspicions by hiding something that you think didn't matter. Let them decide.

I've only run the paperwork for immigration once, but the person I did the paperwork for had three names across various legal documents from various countries with various attempts at spelling. I thought it would totally put red flags all over us, but INSTEAD, they picked ANOTHER new spelling for one of her names and gave that to her for her PR card. They also added 3 years to her age. We went to correct it and the lady behind the desk was like, "so, you COULD correct it, but like, that's gonna cause an audit of your immigration papers, so I'd recommend just not doing that." We ended up not formally reporting the error, and she plans to do a formal name change once she's a citizen so that it's all good in the end.

I would highly highly recommend talking to an immigration lawyer though. They deal with like 10 cases a day, and generally they deal with the tough cases, where it's not as simple as it could be. They'll know the pitfalls. The extra awesome thing they do, is they read everything over and tell you about all the mistakes you made, with like a 48h turnaround time. Costs like $100-$500 ish, depending on how good you are at doing the paperwork the first time around, and how many questions you have.