With more weight you need more volume . While you CAN jam 200 lbs into a 10 foot boat be aware that that length craft was designed for under 120 lbs. You CAN paddle it with 200 lbs but how much fun is paddling a log? The original Wee Lassie was designed to fit the needs of a tubercular 90 lb man.
12’6 is a better choice and I still have reservations. If the 90 lb dog is up front trim is affected because there is not much room to move the dog more midships. And the dog may be uncomfortable enough to stand all the time which is never fun. Heavy weight in the bow vs the stern makes the boat harder to steer. It may wallow all over the place.
Having had dogs in canoes all the time for many years I find that the longer the boat the more comfortable for the dog. But they vary so much in behavior. My 90 lb Golden was antsy in a Merlin II in waves ( she would always stand) but fine in the same length of boat in a Placid Boatworks Rapidfire and the best in a Swift Raven ( which is 15.5 feet long and roomy, a river solo canoe)
So yes weight and distribution of the weight is an issue. Best to take the dog with you for a test paddle.