They're both okay grammatically, but it would sound more natural to natural to use "it" to hold the place of the subject when you're talking about weather:
It's raining too hard for us to play tennis today.
When it's raining this hard, no one wants to play tennis.
Or you could use the people who don't want to play as the subject:
We don't want to play tennis in the rain.
No one wants to play tennis when it's raining this hard.