1
If it will rain, we won’t play.
If it rains, we won’t play.
In a first conditional sentence, use the present simple in the if-clause to refer to the future. Use will in the main clause: ‘If it rains, we will stay at home.’
2
We talked about if we should cancel the meeting.
We talked about whether we should cancel the meeting.
Use whether, not if, after a preposition such as about, on or in: ‘It depends on whether she can come with us.’
Check our grammar lesson on the difference between if and whether.