Liraglutide works somewhat similarly to Metformin, however, it is a daily injection rather than a tablet, increases the production of insulin (which may exacerbate some symptoms of PCOS) and may increase the risk of certain types of cancer.
As it is a very new drug, it has been placed on a cancer register for 15 years to determine whether it will increase the risk or not. It was found to increase a type of thyroid cancer in rats, however, the mechanism by which this happened may not translate into a risk for humans. Serum calcitonin levels (a biomarker for thyroid cancer) were found to be elevated in patients taking liraglutide, however, which would make me concerned about its potential to cause thyroid cancer.
Metformin is generally regarded as a very safe drug and some studies have actually found it lowers the risk of pancreatic and other cancers, though the mechanism by which it does so has not been elucidated yet.
If it were me, I would not be inclined to take the risks associated with such a new drug, which already has a shadow over it, in relation to cancer risks.