Welcome Al, to the our forum. To a large degree, it depends upon the individual dealerships whether or not they will do warranty work on an RV if required. I don't believe it matters if you purchased it the U.S. or in Canada. It will, however, have to pass Canadian certification with regard to propane, etc. Some dealerships will tell you that, because you didn't buy the RV from them, they will turn down your work. This practice goes on in both countries. Others, who seem to have more common sense, will gladly accept it knowing that their service may not be forgotten by you in the future. Even though a dealership sells Keystone products, it is not obligated to do warranty work on an RV that was purchased at some other dealer.
My suggestion to you would be to find a reputable and customer-oriented dealership as close as possible to you, go there before you buy and ask them if they will do warranty work on your RV purchased elsewhere. If he says "yes" ----- problem solved.
2008 Cougar 5th Wheel 27RKS
2005 2500 GMC Duramax