Do not clean the suit first - the problem is given by the fact that the canvas was drenched, not the fabric. A well made chest piece on a suit is the result of various manipulations, including shrinkage, so that only a good tailor will know what to do. If you feel that there was also some dirt from the rain, go for a sponge and press. FYI only a tailor will press correctly a suit (lesson from my late grandfather and his (also my first) late tailor).
7/15/10 at 9:40am