HOW TO OBTAIN PERMITTED ENTRY NOTICE IN WRITING IN ADVANCE TO TRAVELS?

Hey guys!

My company is flying in a USA citizen for a performance to Canada this summer and we are requesting he submits some sort of written confirmation that he will be able to come to Canada for the show. At first we thought he could use an electronic travel authorization but apparently thats not right. What can he do? He has been charged with a crime but found innocent, not sure if that will affect anything. He has no criminal record besides that. 23 year old male, only flying in for the performance then leaving. Please help. Thanks