By all reports the Kaanul (or "Snakes") empire was something quite unlike any other Classical Mayan state. It was more organized and larger (at its height ruling over a realm of some 1.75 million people, 250,000 of those city dwellers) than anything that had come before.
For some centuries, the Kaanul competition with the powerful city of Tikal was the dominant force in Mayan politics, with both cities building alliances with, sponsoring putsches in, or outright conquering other Mayan cities, with even powerful cities like Copán subject internal violence sponsored by the competing powers.
The Kaanul would finally rise to supremacy when King "Sky Witness" crushed Tikal in battle in 562. However, this period of ascendancy would only last 133 years. It would end in 695 AD with another battle with Tikal - this one under the obese and likely diabetic King Yuknoom Ixquiac (or "Jaguar Paw Smoke"). After this, no comparable Mayan empire arose until the Chichen Itza built her empire in the Postclassical period.
What makes the Kaanul's fall particularly interesting is that the weak organizational abilities of late Cassical Mayan polities seems to have played a big role in making the Mayan collapse after 900 AD so bad. Better organized polities would have been able to institute food and water management policies to lessen the severity of the disaster. And the Kaanul kingdom, had it survived until 900 AD, seems to have possessed the requisite organization.
So let's say that Yuknoom Ixquiac (who in his younger years seems to have been a capable enough military commander) eats less soft tomales and avoids his diabetes. When the briefly resurgent armies of Tikal seek battle with him, it is they who end up getting crushed and the king of Tikal gets sacrificed. Tikal thus continues its decline and the Kaanul kingdom continues to solidify its power.
By 900 AD, it would probably be on its last legs, but let's say that it still has the authority to get the governors of the satellite cities (the Kaanul allowed only one king - the Kaanul king of kings - rulers of subject cities were not allowed to be kings) to institute some water management and food storage and rationing policies. Most likely the Kaanul fall during the period of environmental stress (in 900 AD their empire would be 338 years old - most empires don't make it past 350 years). What sort of legacy would this more organized late Classical Maya period have and what sort of legacy would a less severe Mayan collapse have?
My first thought is that whichever European nation sends conquistadors in this ATL, the Mayan region would likely fall more easily (since a more centralized civilization is a more easily conquered civilization) and likely more important during the colonial period, due to greater population and wealth.
fasquardon