I have had lots of experience with rust living in Eastern Canada. The problem with replacing the wheel cylinders is that invariably the lines will twist off going into the cylinders, so you can expect to have to replace your lines back to the block if you haven't already. Heat and a 6 point socket may help you get the bleeders loose, but be prepared for them to break off (ie. buy the cylinders, return them if you can get the bleeders loose). In my younger years I did bleed brakes through the fittings where they enter the cylinder once as a an emergency fix (bleeders twisted off). It seemed to work OK for the few days I drove the car until I replaced the parts , but I obviously can't "recommend" this practice.