At the border between stars and planets, the existence of brown dwarfs have been predicted for 50 years, but these elusive stars have been discovered only recently, in 1995. Only a few hundreds are currently known and their study has led to advances in fields such as star and planet formation theories, the physics of degenerate stellar interiors, and that of very cool stellar atmospheres. I will present the methods and first results from a wide field survey for cool brown dwarfs with the MegaCam camera on the CFHT telescope, the Canada-France Brown Dwarf Survey. Our objectives are to find ultracool brown dwarfs and to constrain the field brown dwarf mass function thanks to a larger sample of L and T dwarfs. I will describe the candidates selection from CFHT/MegaCam i' and z' images using optimized psf-fitting module integrated to Source Extractor. I will then discuss the first results from this survey that currently covers more than 550 square degrees, and has lead to the discovery hundreds of new brown dwarfs candidates. The spectroscopic follow up, mainly carried out with GNIRS and NIRI at Gemini, showed that some are among the reddest and farthest brown dwarfs currently known. I will conclude with the discovery and spectroscopic characterization of the coldest known brown dwarf, CFBDS J0059,uncovered during the first phase of this survey.