I should have just looked at the latex color, but as far as I now, L. biennis has glabrous stems, while L. canadensis is either hirsute or not.
leaf does not match my reference for
Lactuca canadensis is a species of wild lettuce known by the common names Canada lettuce, Canada wild lettuce, tall lettuce, and Florida blue lettuce. Its true native range is not clear, but it is considered to be a native of parts of North America. It can be found in other parts, and on other continents, as an introduced species.