  Given an oriented surface S with base point * on the boundary, we introduce
for all N>0, a canonical quasi-Poisson bracket on the space of N-dimensional
linear representations of \pi_1(S,*). Our bracket extends the well-known
Poisson bracket on GL_N-invariant functions on this space. Our main tool is a
natural structure of a quasi-Poisson double algebra (in the sense of M. Van den
Bergh) on the group algebra of \pi_1(S,*).
