Collies tend to be affectionate, friendly, energetic, and playful dogs. They tend to get along well with children, other dogs, and other pets. They are easily bored and are happy to have others to play with and activities to do.
Should a Collie Mix take after their Collie parent, you should be able to expect a similar temperament. But, the other parent breed will introduce their own potential traits and quirks, so you do want to ask the breeder about them.
You can also meet the mother in person to see what her temperament is like and what behavior she is modeling for her puppies. The breeder should have started some socialization and training, but it is up to you to continue to train and socialize a puppy once you get them home.