It's clear from the way Harris holds the canoe paddle that he is not an experienced canoeist.
Canadians would rarely refer to a retreat by the lake as a cabin, but rather, as "a cottage".
When the two Martins are walking in the woods with the canoe, Steckert refers to the canoe paddle as an oar.
When kid Martin makes the car take a halt to urinate, there was not enough time that he could have unzipped, urinated, zipped. He just speaks for a few seconds, and then elder Martin finished the quotes, but total time was still very less. Could be that the kid had no need to relive himself, he was planning to run away again, but elder Martin crushed his plan, so the kid didn't urinate at all.