Canibals exist in real life. How does making them be a different species change anything?

@JDługosz well for a start they wouldn't be cannibals any more...

I mean they are intelligent beings that eat humans.

Humans eat meat, so they already qualify. Are you particularly worried about a species which is capable of quickly taking down an unprotected human, like a tiger or bear can?

There is one place on Earth where your intelligent carnivores might have evolved without contacting humans until recently and that is Antarctica. The interior of Antarctica is ice-free. A frigid desert. Of course, it would have to be a different Antarctica from the one we know. It would have a sufficiently rich ecology to support the carnivores as its apex predators. It would change polar exploration drastically. The co-evolution model is doubtless the better one.

Read Star Trek:Gemworld.

@CortAmmon Yes, this question is about a non-human, intelligent carnivore that, to borrow your words, is capable of quickly taking down an unprotected human.

Will the carnivores always win in a fight or do humans have weapons?

@BrianRisk You may assume that the humans are similar to those of our world.

Many authors doing this make the aliens a proud warrior race guy - see for example, the Kzin. You might also consider looking up Decision at Doona, Caitians, Dragaera, D&D species (e.g. Rakshasa), Krogan, Uplift universe etc. there is hardly a shortage of examples! Mostly, they're just treated as furry humans and no-one bats an eyelash

Dogs. Dogs. Dogs. We love dogs. Dogs love us. Dogs are smarter than $SPECIES_TO_BE_INSULTED

There is only one step: Don't eat your friends.

@a4android "The interior of Antarctica is ice-free" what now?

The answer to your question is dogs. There is absolutelly no reason that makes it difficult to coexist with carnivorous.

Don't forget the other requirements: sapient, intelligent. This reads as "How would we have evolved if dogs could talk". Obviously, we would have been trained to use poop scoopers much sooner.

@njzk2 Yes sections of the interior of Antarctica are ice & snow free. I was gobsmacked when I learned that, not that I'm an expert about Antarctica. So an alternative Antarctica with the ecology to support carnivores isn't entirely impossible. But it would be a major exercise in worldbuilding.

We do coexist with an intelligent carnivorous species: humans.

@reinierpost Please read more than the question title.

@Michael Kjörling I have. I honestly don't see how the other species being non-human fundamentally changes considerations regarding how the two can live together.