The new Seaway Twin pipeline will almost double the amount of heavy Canadian crude coming to Gulf terminals and plants to about 400,000 barrels a day starting in January, according to Calgary-based based ARC Financial Corp. The shipments are growing even without the Keystone XL pipeline, which has been delayed for six years because of environmental opposition. The Canadian supply will square off against crudes from Mexico and Venezuela that have traditionally fed refineries along the Texas and Louisiana coasts.