I hate to say it, but you're not likely going to be camping in Algonquin on May 3rd this year. But to answer the question, a wetsuit and water shoes. Yes, his feet might get cold stepping in and out at portages, but you're stepping out into shallow water at worst, and it's not going to be all that cold. Or a wetsuit and neoprene socks I suppose, but personally speaking I don't want to take the time to switch between those and my shoes on both sides of a portage.
Chest/hip waders sounds super dangerous to me. What happens if you dump into the lake? You'd be too heavy to ever get back into your boat or even try to swim for shore.
