RussSeaton, Thanks for your answers. I'm from France but I not in France, and I'm not leaving near coast anyway :-)
I will try to extent my visa when I will be in Canada, but if I can't I will have to take the road. I try to not using transportation, except my feet, bicycle or canoe... and boat to cross ocean!
Rain, cold, snow, ice, wind are the problems you will face. Since you are from France, you should have a good idea of the weather in the USA. France and the USA are somewhat similar in latitude. Latitude being how far north of the equator you are. Northern France has winters similar to what the north half of the USA has. Southern France, near Spain and the Mediterranean have winters similar to what the south half of the USA has. Although southern France is probably not as warm as southern USA. Imagine walking or biking from Belgium to Spain along the Atlantic ocean in mid February and you will have a good idea what it would feel like to bike from Vancouver Canada to Mexico along the Pacific ocean. Miserable in the north and better in the south if you start the middle of February.