The only payment option is by U.S. credit card (only States and Zip codes allowed). There are many Canadian visitors to the USA who would probably like to use your sitting services but there appear to be no other payment options available!
I would initially contact Rover Support to see if they're able to accept your credit card information on the phone. If they're able to process it on the phone, then I don't see why you wouldn't be able to book a US-based Rover sitter the next time you visit.
I would not take on a client from Canada until I am sure it is allowed. Since it is a different country, they would have to go by our rules.
I would suggest loading a prepaid Visa or MasterCard when you travel and using that for Rover bookings, listing the address where you will be staying in the US on the prepaid account. If you can use a friend or family member's US address that would be ideal since you could keep the same prepaid card for multiple visits and reload it as needed.
An interesting workaround. Kudos for imagination. However, I would check on Rover's ability to take his credit card info over the phone first. Even though Rover doesn't provide services in foreign countries, there's really no reason why its payments processing system should be so limited.
We own a home in Bellingham and are not going anywhere......how else do we pay???