Papers needed to cross into Canada with 2 dogs?

Our dog always sits right up front on the arm rest where she can be easily seen. We crossed into Canada and back twice last year on a 2 month trip. Two years back we also went on a 2 month trip crossing into Canada. Not once have we ever been questioned about our dog, including one time when the Canadians spent over 45 minutes going through our RV.
We always carry proof of rabies shot and the usual yearly check ups.