Are you more likely to have incontinence if you deliver a big baby?

Depends. There are many factors that go into incontinence. Some people deliver small babies but because of genetic differences in their tissue they can develop incontinence. Large babies with difficult deliveries is a risk factor but does necessarily cause incontinence in all women.
Most of the time. Childbearing causes stress on the pelvic floor muscles and support. As one ages it is more likely to have pelvic floor relaxation and mores if there has been childbearing. Pelvic floor muscles can be effective in prevention and treatment of this inevitable relaxation. The bigger the baby, the more stress and strain on the pelvic floor.