Netanyahu, Israel's longest-serving leader, has been charged on several counts of corruption but is battling fiercely to maintain his grip on power.
After inconclusive elections in April and September, latest opinion polls put the two opponents neck and neck in a gruelling political triathlon.
According to the projections, Netanyahu's right-wing Likud and Gantz's centrist Blue and White alliance would each win 33 seats in the 120-member Knesset, Israel's parliament, in Monday's polls.
That result would be almost identical to the previous round, after which each leader tried and failed to form a government.
In previously unannounced television interviews aired separately Saturday evening, Gantz and Netanyahu ripped into each another.