Len Cariou—Stephen Sondheim’s original Sweeney Todd—plays the title role in Sea Dog Theater’s revival of Tuesdays with Morrie by Jeffrey Hatcher and Mitch Albom. Amid the stark, solemn beauty of Charles Otto Blesch and Leopold Eidlitz’s Romanesque-revival chapel at St. George’s Episcopal Church on Stuyvesant Square, director Erwin Maas has built a fleet, music-filled production around the distinguished Canadian actor, who’s sharp and feisty at 84. In the role of a professor experiencing the galloping effects of amyotrophic lateral sclerosis (also known as ALS or Lou Gehrig’s disease), Cariou steers clear of mawkishness with a performance that’s wry and witty from beginning to end.