There are no restrictions at all as far as muzzle-loading rifles are concerned. Even the regulation in parts of southern Ontario re: .275 cal doesn't apply to muzzle-loaders and, of course, you can use a muzzle-loading rifle in an otherwise "shotguns only" area.
In my experience the majority of muzzle-loading rifles used are .50 cal., followed by .54 cal. then .45 cal.
The smoothbore with shot may have a few restrictions:
I believe you would still have to use steel or other non-toxic shot for waterfowl.
For big game hunting with buckshot there may be a restriction on buckshot size. On page 22 of the 2010 Regs it says you can't use a shotgun smaller than 20 ga or any shotgun loaded with buckshot smaller than SG (No. 1 buck).
For turkeys you can't use a shotgun bigger than 10 ga. or smaller than 20 ga. and shot size must be 4,5 or 6.
I'm not positive about the muzzle-loading smoothbore restrictions - the regulations on P22 refer to "shotguns" and "muzzle-loaders" as separate entities. I imagine it would take a lawyer to determine if the regs mean that a muzzle-loading smoothbore is actually a "shotgun".