Yeah I'm going to do that. But I think when you port it sprint cancels it at the same time.
This is correct. If the number you're porting from Sprint is the only one that is on that particular account (eg, this isn't a family share plan with 2+ numbers), the port request will close out the Sprint account. DO NOT cancel the Sprint account or that will potentially cause you to lose the number.
Activate Verizon with a temporary number and keep your Sprint service active. Once you have determined a few days later everything is working with Verizon and you are satisfied, then port the number from Sprint.