/u/grapp

European exploration of the Canary islands preceded the Castilian conquest by about a century. Castilian and Portuguese mariners had explored the islands at various points as far back as the early 1300s.

By the 1340s, several expeditions had been sent from Portugal, Majorca, and Castile. Some of these captured natives to bring back to Europe. At the same time, the Catholic Church became interested in the Canary Islands, in particular the idea of converting the natives into The One True Faith. By the 1350s, Pope Clement VI had issued a bull Tu devonitis sinceritas endowing the princely possession of Canary islands to Luis de la Cerda, a Castilian prince living in exile in France and assigned to be French ambassador to the Pope. The problem was, Cerda was neither in the Canary Islands nor did he have any effective means of conquering it. For that, he needed Aragonese support.

Predictably, both Portugal and Castile protested vehemently. This led to all parties sponsoring expeditions to the Canary islands, with varying degrees of success and failure. These expeditions included the capture of natives, brought to Europe.

So, by the time that Castilian forces landed their force in 1402, there were already contacts between Europeans and natives, and there were surviving captured natives who could translate. These expeditions included Franciscan monks who recorded that they brought along two Guanches -- Canarian natives -- who had been captured and converted in earlier expeditions.

By that point the Guanches were already very aware that Europeans came with goal of subjugating them. So it's hard to answer whether the Castilians tried to negotiate or just attack them directly. You will have to be more specific on which stage / encounter.

Want to know more? Fernandez-Armesto's Before Columbus: Exploration and Colonization from the Mediterranean to the Atlantic, 1229-1492 covers this in good detail, including the rivalry between emerging Iberian powers.