Here are the facts:
All USA spec Honda EU2000i models have always had parallel receptacles. The very first model was the only model, and when you connected them together, you could only get a tiny bit more power due to the size of the breaker. At the same time, Honda offered the EU1000i and the EU3000is.
In Canada, similar models were introduced. The EU1000i was launched first, and it had parallel outlets, but when the EU2000i was going to be introduced, CSA regulations would not permit it, so the parallel option was removed from the planned specifications. All Canada-market EU2000i do NOT have parallel connection. All Canada-market EU1000i continue DO offer parallel connection.
Next, back in the USA, Honda created an external parallel kit with a 30A breaker and 30A receptacle. This allowed a parallel connection between two EU2000i units with a full 30A of power. These external parallel connection boxes were made by Gen-Tran and Relliance companies, and have been discontinued, but still offered online and allow any two standard EU2000i to be connected together.
A few years later, Honda introduced the EU2000i Companion. This model featured an built-in 30A receptacle, and eliminated the need for an external parallel box. You could now just connect the parallel cables between two EU2000i units (base model and Companion) and get the full 30A power out of the Companion's 30A receptacle. The Companion eliminated one of the two 15A receptacles and the DC charging receptacle. The Companion has a list price about $130+ than the standard EU2000i.
Next, there is the Camo EU2000i. This is exactly the same as the standard EU2000i, but the outer covers are trimmed in a camouflage scheme.
You may use parallel cables between *any* two models of EU2000i. For best results, at least one should be a Companion, as to take advantage of its 30A receptacle. Otherwise, you'd be limited by the smaller breaker and receptacles on the other EU2000i models.
All Honda EU2000i models have cast-iron cylinder sleeves and a 3-year warranty. They are manufactured in Japan.
Full details here:
Honda Generators-Robert@Honda
Caveat: I work for Honda, but the preceding is my opinion alone.