Look, we (HMCS Donnacona) used to patrol part of that area from time to time (Richelieu River - tip of Lake Champlain) and I've been on some of those patrols (disclosure: late 90's early 2000's). We had a good relationship with the Coast Guard and Border Patrol, a somewhat colder one with some Sherriff's dept. (some of them are real pricks thinking they are the the sole defenders of freedom or something). But that portion of the lake, near the border, is full of boaters and is not necessarily too well marked (there are no border indicating buoys at all and no large, visible signs ashore). Boaters from both nations drift over the border all the time. However, unless they tried to land or clearly enter the other nation with obvious intent to stay, the practice for Coasties/RCN/RCMP/Border Patrol was simply to approach the drifter and inform them that, perhaps they didn't notice but they drifted into the other nation's waters, then point them the right way.
So this is a change - for the worst - by the Coast Guard, and it fits right in to the current narrative (probably correct) that many American officers serving in US Homeland security feel emboldened by the current US administration to let their "total-prick" side take over in circumstances that don't require it.