The Bible states that the Canaanites had become so evil that He destroyed them and gave the land to His chosen people. He even had them wait as at the time of Abraham their crimes against God had not yet come to the point of annihilating them. The Bible also tells of them losing their land again and again when they turned away from Him. So using the Bible to try and say it’s not theirs is ridiculous. Saying they need to get right with God if they want their land back would be a decent argument.