Frankly speaking, No, you cannot commit any leads number to your client because Google does not commit any fixed figure itself.
But, yes you can share the estimate data to your client according to the keyword planner tool.
The below statement shows in Keyword planner tool:
“Keyword Planner can be used to generate keyword ideas, but it doesn’t guarantee improved performance. You’re responsible for your keyword choices and for complying with our advertising policies and any applicable laws.”