I'll note that, since you've already deviated from the canonical Planet of the Apes by including wizards, I'm not overly worried about continuity. The absence of canids and felinids will leave a gap; nature abhors an empty niche, and given a few hundred years, other species will fill in those gaps, and a few thousand (1800 or so for the original movies, POTA and Beneath the POTA), it's possible that new species would have evolved.
Gibbons, who are apes, but not great apes, would seem ideal for replacing elves in such a setting. Different enough to be way out there. Alternatively, mystic-acrobat would fit, as well...
Monkeys likewise could be used to fill in the demi-humans' roles, should you opt for that.
As for orcs, et al: replacing them really requires picking which element you're replacing.
D&D tends to treat orcs as the "cheap kill" experience fodder, and thus has them breeding much like rabbits. Since they breed like rabbits, why not replace them with rabbits. Some rabbits can get impressive in size - up to several kg in domestic breeds. Really, they would be a better fit for the smaler goblins and kobolds.
Most any natural animal from Cyclopedia, AC9 Creature Compendium, or the AD&D monster manuals, aside from the extinct predators (canids and felinids), work well.
ROUS (Rodents of unusual size) and Weasels will likely fill the wolf niche of hijacker and harrier in North American settings; Badgers, too, will expand their range of prey.
Horses and deer make for great potential monsters. Real world, horses and deer have been known to eat meat in the wild. (cite 1 horses, cite 2 deer) So, having a speciation event where they go back to eating meat isn't untoward. Also, note that precursor horses were omnivores... and some horses still to date grow canines and premolars as a genetic throwback.
Terror Birds, in the absence of industrialized populations, are likely to rehappen, too. Take an eagle or raven, and have them grow huge. Geese and swans are already dangerous. Now, think a raven or crow in the 50-80 pound range, 15' wingspan, smart, greedy, and mean.
Bears are a likely source for megafauna predators.
There are lots of snakes and lizards in North America.
And that's all before any magic stuff.
And so we add magic and radiation
Adding magic, and the radiation from the wars implied by the nature of the changes in the physical environment...
Giant bugs (Keep it reasonable, and you limit them to a couple feet long; adding magic, 8'long roaches).
Land crabs that get huge. Crayfish that decide land flesh is good. 60' Crocodilians and snakes.
Possibly even escaped dinosaurs, recreated by mad scientists just before the ape-takeover.