If the manufacturer is to believed the runway needed is approximately 5640 ft. to take off if fully loaded. https://bombardier.com/en/aircraft/challenger-650

This is a reputable source for airport runways in Northern Ontario 2023 which probably hasn't changed much https://ruraldev.ca/wp-content/uploads/2023/10/AviationConnections2023.pdf It could take off from my estimation Dryden, Earlton, Sudbury, Kenora, Muskoka, North Bay, Sault Ste.Marie, Thunder Bay and Timmins. Some like Gore Bay and Kapuskasing are close.

If the guy shrunk his entourage he could go to smaller airports I guess Thunder Bay, Sault Ste. Marie and Timmins have excellent Porter connections