Assuming you narrowly dam up the canal near the ship to contain the brine, no I don't think so. Seawater is 3% saline and saturated brine is 26% saline, so you'd probably have sufficient mixing within the canal itself once you open the dams. The canal is 120 miles long and I can't imagine you'd dam up more than a third of a mile at maximum. But it would take a whole hell of a lot of salt.

Yes since the salinity transfer from the canal into the Mediterranean Sea is already enough to make species from the Red Sea colonize the east Mediterranean. The Aswan dam reduced further the amount of freshwater coming to the area. So I would guess adding more salt wouldn’t be too good for the eastern Mediterranean.