Cantina is one of my favorite places in the summertime. Their back patio area is awesome. It's filled with high top tables, a covered bar area with stools, and a little place to lounge at the end of the bar with a couch and table.
My favorite time to go is during happy hour and get pitchers of sangria. I also enjoy their queso and guacamole.
Honestly, the staff can be hit or miss. Sometimes we've had great experiences with the waitstaff and other times they have not been friendly at all. The vibe inside the restaurant is kinda dark and trendy and hipster. The front room is the bar area with a couple two person high top tables, then the back room has larger high tables if you care to go for dinner. I've ordered their tacos on multiple occasions and they are decent. I've definitely had better tacos but if we are hitting up happy hour we generally order tacos too.
If you're going through lawrenceville it's definitely a cool place to at least try once (especially in the summer) if you're looking for neat place for a drink.