While canids are nowhere near my top priority for new carnivores, these are my top choices:
1. Black-backed jackal - I have seen these at a couple of places before (my local zoo, Colchester, had a group of them for years and I also remember them at Amersfoort Zoo in the Netherlands), and they have recently been brought back to the UK at Hamerton Zoo. I think they are very pretty animals and wouldn't mind seeing them at all.
2. Bush dog - Colchester Zoo has now got a lovely enclosure with a big breeding pack of bush dogs - they are amazing little animals and would add quite a bit to a South American zone in the game, as they would provide a true Amazonian rainforest species to complement the grassland-dwelling maned wolf.
3. Iberian wolf - I remember when Colchester Zoo had these guys as well. They are quite different in appearance to many other wolves, with a very rich brown coat. They are one of the wolf types managed in a European breeding programme, and would be my favoured option for an updated wolf model.
And then, considerably lower down the list...
4. Mainland raccoon dog - Only seen the species once (my college had a couple of them in their animal care department), and I personally found them to be rather tatty looking and uninteresting creatures. Still, they are around so I would begrudgingly accept them.