Because the tearing of the St. Lawrence seaway will begin as soon as the stretching of the Atlantic occurs, land along this seaway will not submerge nor will any noticeable influx of ocean water occur, as the influx will be filling the new river bed area, now to become more of a lake. The tear will occur principally where the St. Lawrence seaway now runs, as this is a low point only because of the existing tear. Weak spots are deep within the rock strata under the river bed, and the tearing is less of a deep rift than a pulling apart in many places, so the surface seems relatively smooth. Beneath this tear are many feathery fingers of rock, reaching toward each other, soon filled with hardened magma to solidify. Thus, even though Montreal is surrounded by water, it will simply find itself more of an island than another Atlantis.
Note St. Lawrence Seaway commentary.