Jehovah did not decide the fate of the Canaanites for them.
Then, when the other cities attacked Gibeon, the Israelites rightly felt a moral obligation to defend them (Jos. 10:6-8).
Gibeon was spared the peril that the rest of the country suffered because, in their own words, they were ‘plainly told that Jehovah […] commanded Moses his servant to give Israel all the land and to annihilate all its inhabitants,’ (Jos. 9:24).
Thus, instead of arrogantly waging war against God himself, they laid themselves at the mercy of Israel and were indefinitely assigned the role of temple servants (Jos. 9:25-27).
The fact that Jehovah did extend considerable mercy toward the people of Gibeon, even allowing them the privilege of performing duties directly related to sacred worship, highlights his willingness to set aside the execution of his own judgment in order to favor those who seek him out sincerely (Ps. 86:15).
It is different, though, in the case of those who ‘allow their hearts to become stubborn.’
We do not need to be Canaanites or God’s sworn enemies to fall into this trap of obstinate arrogance.
Whether or not we witness God’s saving hand does not depend on who we are or where we come from.
It depends on whether or not we individually heed his words to ‘cleanse our hearts and stop being so stubborn,’ (De. 10:16).