Need info about Canadian lease agreements and co-signing.?

Here's the scoop. My boyfriend is the co-signer on a lease with a former friend. They are on good terms right now, and it seems as though the former friend has defaulted on the lease payments. It's been about a year and a half since the lease was signed, and it's for a four year term. As the cosigner, to what extent is my bf liable? Will the dealership sue the primary signee first, or how does that work? Besides kicking himself for a) cosigning and b) not redoing the paperwork as soon as the friendship went sour, is there anything he can do to prevent getting penalized? Input would be appreciated!