77 mins is darn short. I wouldn't count on it. The last time I arrived at CLT internationally it took a solid 60 minutes to clear C&I. And yes, you WILL need to clear customs in CLT regardless that your final dest. is in Canada.

You will need to claim your bags at the carousel, and recheck them with the carrier. The bags will be waiting for you either on the carousel or likely on the floor, as other international flights will have overflowed the carousel... So they stack 'em up on the floor.

HTSC