Sign describes a "trophy trout section" for a distance of about 4.8 miles downstream (west) of this dam as the crow flies, perhaps a little over 5 miles if you add in the river's curves.
Sorry, but I'm not an angler myself, so I can't provide anything but the location.
USGS Real-Time Water Data link is for the only point available on the Missisquoi (more than 25 miles upstream).
Kane Road Bridge is the first crossing west of here (waymarker here). Parking is available at both ends of the defined section.