The Tours route goes through Bordeaux. To join the Norte there is several options, you can walk a link up section between the Tours route and the Voie Littoral, and from there it goes to Bayonne and leads directly to Hendaye and Irun, I have walked on the Voie Littoral and while most of it was on quiet soft surfaces through forests, you would be on asphalt to the Spanish Border from where you join it. The other options are to walk to either St Palais on the Tours route and follow local walking routes to Irun, many pilgrims do this or walk to Saint Jean Pied de Port and follow the route which links up to Hendaye along the foothills of the Pyrenees.
Good Luck and Buen Camino