Leave it up to them to ask more details. I wasn't a speaker at my last conference, but I could have been. But my conversation at the border was something like: "Why are you visiting Canada?" / "To go to a conference" / "Where is the conference?" / "Downtown" / "How long will you stay?" / "3 days" / "Ok, welcome to Canada".

When US CBP asked if I was "presenting, or attending", I did NOT take the opportunity to explain that everyone was expected to participate and present :)

I know that b/c my lifestyle is sometimes "unusual" while at the same time I have a strong inherent tendency to be very correct and "overly" honest. :D

"Why are you visiting Canada?"

"I"m here for a conference"

"What's the conference about?"

"Computer vision, you know, programming research"

"How long are you staying?"

"A week"

Stamp

There was a point on the outbound journey where they were checking everyone's passports by the scanner (i.e. you'd go through and everyone would set the alarm off, but it seemed to be a passport check rather than anything else), as soon as they saw it was British they lost interest.

It does, the lineups at Toronto's Pearson Int'l airport are longer for Canadians in my experience.

This is very good advice, anyone prepping for depositions would have heard it already but it works very well for border personnel too.

"On vacation."

Done.

On the other hand, I've gotten across with no delay at all by saying "I'm picking up a friend at the Vancouver airport" and "I'm going to go buy this drill press off of Craigslist -- see this printout?" Neither of those is illegal, and in neither case can they expect you to have hotel reservations or know any Canadians, etc.

One of my favourite parts about driving to the border is going through scenarios with my passengers, and how to answer each question.

Honesty might get you in trouble, but thats still probably a better place to be than trying to lie your way out

So, sort of the same strategy used for patent claims?

The thing is, these laws are not meant to apply to "you", and the enforcement officers understand that - these laws are designed for people from lower-income countries seeking prolonged employment, i.e., economic migration; not first-world travelers that happen to earn some money while on the trip - the immigration officers entire reason of existence is to detect and prevent the former, while the latter doesn't matter, so they understand all the factors but since it's hard to draw an exact line, these laws do apply to e.g. conference speakers as well, and if you explicitly disclose to them that yes, you intend to do some paid job during your trip, then they pretty much have to deport you, and it's much harder for them to turn a blind eye and follow just the intent/goal of that law.

I wonder if the immigration officers described here actually thought they were being fair, because they were applying the law as written to a white American, even though the law was not written to keep out white Americans.

Which is to say, we can be horrified by the attitudes of the officers, but it's the law that needs to be changed, not their attitudes.

I remember once we were traveling by road to Waterloo, to meet some buddies. We picked up those 1.5L bottles of booze, one each. That's 6L of booze in the car. At the Buffalo border, the dialog went like this:

Guard: where are you going?

We: Niagara Falls, just for the evening (we were afraid that they might now allow us in if we admitted to partying in Waterloo)

Guard: are you bringing in anything?

We: This booze.

Guard: As a gift for someone?

We: No, just for ourselves.

Guard: (incredulously) You'll drink that by yourselves?

We: Yes.

Guard: (rolls eyes) OK, come on in.

I was flying home from England to Sweden and going through the inspection before departure. The guy checking me could tell that I was upset about it all, having to remove my belt and maybe even my shoes. When we were done, he had the greatest line: "Thank you for your cooperation, from Mr. Obama."

We all play the game, but to not know the game is surprising. Hack the system, sure. But know you are hacking at least.

(I'm assuming OPs presentation was work related)