Don't lose sleep over it, cops really don't care how much the tires stick out on a Jeep yet alone Canada Customs, I am sure they would not know what to do with it or even look at it unless they suspected contraband or guns !
DO NOT TRY AND BRING A GUN INTO CANADA OR YOU WILL BE ARRESTED RIGHT ON SPOT !
I drive my 32 Deuce Coupe all around and never get pulled over with it and it's kit car registered in 1986 ..
I see no sense in calling the border , they will not know what to do as they aren't cops , I have a cousin that is a border agent and will ask him about it and post back but I think I already know what he is goind to say
Here are the fenders on my 32, or lack of :