I take it that more than just you and your brother are taking this trip!
Really can't answer your question legally but when I was a kid we used to go to Canada with the boat on top of the car (loaded) using cartop carriers, that was back when they made cars out of metal
I am sure we were overloaded as we could be and real lucky we never had any problems but that was back then and things have change a heck of a lot.
Safety first I guess the next question is what is the trailer rated to haul? Tire rating etc. heck I have seen these guys hauling canoes stacked 6 high x3 wide!
Good luck on the trip, know you are gonna catch fish, one of these days Ima gonna go back up there!