A Lowland is an area where the land is at, near, or below the level of the sea, and where there are not usually mountains or large hills.  

“St. Lawrence Lowland is a plain along the St. Lawrence River between Québec City in the east and Brockville, Ontario, in the west, including the Ottawa River valley west to Renfrew, Ontario. The lowland’s total area is 46,000 km2 (5,000 km2 of which is in the United States). It is 450 km long west to east and 100 km wide in the western half, narrowing to 35 km at Québec. In addition, an arm extends 130 km south into the Lake Champlain valley.”
Source: Elson, John A.. “St. Lawrence Lowland”. The Canadian Encyclopedia, 15 May 2019, Historica Canada. https://www.thecanadianencyclopedia.ca/en/article/st-lawrence-lowland. Accessed 31 March 2020.


Basses-terres du Saint-Laurent:
bandes de terres qui longent le fleuve Saint-Laurent. Les colons se sont établis en premier dans cette région à cause de ses terres fertiles et de son relief plat. Source: https://primaire.recitus.qc.ca/lexique/liste/b

Basse terre – Une zone de terre ou un territoire qui est plus bas qu’une autre région.