Well, it looks like those days are back with Dash and Terminal.
While it takes 3 pylons to wall off behind the mineral line on this map, it is the first map in the map pool since daybreak which allows such a favorable wall off in terms of attack surface, and wall off reinforcement possibilities. The map, unlike Daybreak, isn't perfectly symmetric so the cannon rush spots are different in each spawn location.
General ideas
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Build order:
- 9 pylon close to your nexus
Why close to your nexus and not on the ramp:
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Holding the ramp would only be useful if your opponent gets a stalker out and attacks you. However, this is very unlikely because of how quickly this cannon rush hits, unless you completely fail the build.
At around 1:10 (assuming decent worker stacking), a few seconds before your 10th probe pops out, select a probe and send it across the map.
If you're lazy, you can just rally the 10th probe.
(2 chrono on probes)
- 13 forge
Stop probe production at 13.
You wanna send the probe immediately in the back of your opponent's mineral line and build the 3 pylon wall off as explained below. Then as soon as the pylons complete, you start the 1st cannon. A 2nd probe should also arrive later on to build additional cannons outside of the wall off if necessary.
How to cannon rush the 12 o'clock spawn
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Wall off and pylon placement order:
The amount of probes marked close to each pylon is the maximum amount of probes which can attack the pylon at the same time.
Because the 3rd pylon can be attacked by 6 probes at the same time (it requires a bit of micro though, a+click from the mineral line isn't enough), it will fall rather quickly. Luckily you can build a 4th pylon after the cannon which will fully prevent probes from reaching the cannon.
After the reinforcement pylon, start a 2nd cannon behind the first one.
Notice that the cannon in the back is in range of the nexus. Because of this, you don't need to send a 2nd probe early on. Also, 2 cannons kill a nexus fast enough to the point that building a 3rd cannon isn't necessary unless your opponent is still attempting to break the cannon rush.
Sending the 2nd probe at around 2:30 is probably ok.
How to cannon rush the 3 o'clock spawn
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Wall off and pylon placement order:
The amount of probes marked close to each pylon is the maximum amount of probes which can attack the pylon at the same time.
As you can notice, each pylon can be attacked by a very limited amount of probes. The most vulnerable is the 3rd one. Luckily, you have the probe down there as well. If the pylon gets killed, hold position your probe. This way, your opponent's probes will have to kill it before reaching the cannon. By then, it should be finished.
Since you only have room for 1 cannon, it's important to have the 2nd probe reach the base at a decent timing. Therefore, rally your last probe (the 13th) towards your opponent's base.
Follow up
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If the wall off doesn't go up, you're dead. I guess you can try to rush to DTs while massing cannons on your main base ramp to defend from the counter attack.
If your opponent is able to break the cannon rush - which shouldn't happen once the wall is up - it can turn into an even game if you gained a large economic advantage by killing lots of probes (remember that you are massively behind in tech).
In that case, you proceed the game as normal, getting a gateway and gases. If you think you're decisively ahead, going 4 gate is the easiest way to close the game.
If the cannon rush isn't broken, your opponent is forced to rebuild his nexus elsewhere.
You should use your cannon rushing probe(s) to find out where his new base is located as soon as possible.
Your opponent could be tempted to build it in a gold base, in which case you can just cannon rush it from the high ground. Otherwise, get a gateway and start teching to warpgate. In this situation you should be massively ahead in general, because the cannon rush hits so quickly he shouldn't have the money to build the core/start warpgate, and obviously he loses a ton of mining time..
If your opponent gets a zealot out and/or wants to all in you with a probe pull, start a cannon at home and you'll be fine. You don't need to be 100% sure he is doing it. Having a cannon to protect your mineral line is an efficient safety precaution which comes useful through all the game as well - DTs, oracle, etc.
Finally, remember that you have that forge, you should exploit that by getting early upgrades if possible. I've had crazy games where I got +3 while staying on 1 mining base the whole time after a cannon rush which turned into an even game.
How to defend it
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I honestly doubt you can defend it if the cannon rusher gets the wall up and knows how to execute it properly.
However, you can blind counter this with building placement. The goal is to place your first pylon/gateway so that your opponent can't get a proper wall off. Here are my examples.
12 o'clock
3 o'clock
If you see a probe coming inside your base at a suspicious timing remember that he will still cannon rush you if he opened forge, probably trying to find another wall off, even using your buildings as part of the wall. These wall offs shouldn't be favorable and you should be able to break them by pulling probes while chronoboosting a zealot out.
This cannon rush can also be easily countered if the defender immediately sees the probe, realizes that it's a bit too early (nobody scouts earlier than 13 scout in PvP, and the probe comes ~25 seconds faster than a 13 scout on a regular map) and immediately pulls a couple of probes in the back of his mineral line for safety, preventing the wall off from going up.
Why does it work?
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There are different reasons depending on the spawn locations. In general, the boss cannon rush is stronger than a regular cannon rush because the cannons hit the mineral line immediately, preventing your opponent from mining, as well as the nexus.
In the 12 o'clock spawn location, it works because you can reinforce with a 4th pylon in the back of the most vulnerable pylon, furtherly preventing probes from reaching your cannon, and a 2nd cannon in the back of the 1st one which is in range of the nexus.
The strength of the 3 o'clock spawn cannon rush, instead, lies in the pylons' ridiculously small attack surface, as well as the hold position probe trick behind the most vulnerable pylon which can buy additional time for the cannon to finish.
Finally, once your 1st pylon goes up, if you follow the correct pylon placement order, your opponent won't have time to prevent the placement of the 2nd and 3rd pylon, unless he pulled probes preemptively.
In the 12 o'clock spawn location, it works because you can reinforce with a 4th pylon in the back of the most vulnerable pylon, furtherly preventing probes from reaching your cannon, and a 2nd cannon in the back of the 1st one which is in range of the nexus.
The strength of the 3 o'clock spawn cannon rush, instead, lies in the pylons' ridiculously small attack surface, as well as the hold position probe trick behind the most vulnerable pylon which can buy additional time for the cannon to finish.
Finally, once your 1st pylon goes up, if you follow the correct pylon placement order, your opponent won't have time to prevent the placement of the 2nd and 3rd pylon, unless he pulled probes preemptively.
Replays
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I'm not the type of guy who does this every single game so I don't have lots of replays, but there you go.
http://ggtracker.com/matches/6106766 - 3 o'clock
http://spawningtool.com/28855/ - 3 o'clock (LotV beta)
http://ggtracker.com/matches/6106786 - 12 o'clock
http://spawningtool.com/28854/ - 12 o'clock (LotV beta)