no paperwork, US side couldn't care less, you won't even see them on your way back, Canadian side will collect taxes ( keep your invoices) and check if animals are on CITES list or not, pacman frogs are not. make sure you tell them that it is not for resale but you personally. Commercial imports do require tons of paperwork and permits.

all info is recent, i got frogs and snakes this way at the end of March. but we were more then 48h in US, so no taxes for us