Coyote; but it's a selfish choice since they'd be another North American species. They're obviously a lot less distinct than the jackal, but it is what it is. I'd be happy with either, but I also think they're fairly low priority amongst canids. And unfortunately I do think we could stand to have quite a few more canids.
The two canids I really want are the raccoon dog and the red fox, which I suppose would also be my two favorite species not in the game now that I think about it. I don't personally understand the massive appeal the maned wolf seems to have, but it's fine as well, I suppose. I like bush dogs a lot, but I imagine they'd be a lot lower priority than the maned wolf for whatever setup gives us the next South American canid. And I like bat-eared foxes a lot too, but ultimately I think 3 fox species is probably going to be sufficient.
tldr give us raccoon dog, red fox, and maned wolf