Canadian water starts about a mile north of us. We use the Canadian CanPass to legally enter Canada without checking in and, in fact, were just spot-checked by authorities last week and everything was in order.
US officials in our area have recently made a big deal over the need for returning US citizens to have in their possession an I-68 permit. I used to get these some years ago until one time when the agent couldn't readily find the forms in his desk drawer and mumbled something about not really needing one in the first place. Upon questioning him, he said the I-68 permit is an Immigration form and that Immigration Laws do not apply to US citizens (i.e.- we are not immigrants). As soon as it is determined you are a US citizen, they can do nothing to you under Immigration law. I haven't gotten one of their permits since, nor do I intend to despite their recent threats of dire consequences. We have, however, started carrying our passports with us.
Customs law, I believe, is a different matter and here I might have my butt hanging out a bit. But then again, we don't often make landfall when in Canadian waters (although I don't really know if that matters) and if we were to, US Customs would have a hard time proving it upon our return.
I guess what it boils down to, is every geographic area is probably a bit different. I read the requirements about the need for licensing a VHF when cruising in foreign waters, but that only applies if one calls at a foreign port or talks with a foreign station. There are no foreign ports on the Canadian side of our lake and I almost never talk to anyone on the VHF anyway, so I guess I don't need a license. Those of you cruising from Washington State to Vancouver or Victoria might well be advised to have one. Especially if you're piloting and 85-footer!