I'm a dental hygienist, but I don't know much about "doggie dentistry." The canine is a very important tooth in humans as well. If it is extracted, it may affect the dog's ability to eat certain things, as well as the dog's facial appearance. The space may also cause the other teeth to shift. On the other hand, a tooth that has had root canal treatment will need some sort of restoration, like a crown, placed on top of it. In the short term, the extraction is cheaper, but you may run into other problems in the years to come. Your dog is still young. Ask the vet dentist for recommendations and options. Also, if the tooth was broken off to the gumline, the crown will probably need a post to hold it in, which will also increase the cost.