Ways to get into Toraimarai Canal:
1) Get a WHM, RDM, and BLM and go through the 3 mage door in Horo. Ruins.
2) Complete Windurst 3-2 to get a portal charm key item and use that to go through the 3 mage door in Horo. Ruins. You will need a WHM, RDM, and BLM to complete Windurst 3-2 unless you skip the mission and then come back to it in which case you can solo it.
3) Complete the Rhinostery quests listed by Esdim:
1. Food for Thought
2. Overnight Delivery
3. Water way to go!
4. Blue Ribbon Blues
5. Toraimarai Turmoil (only need to flag this quest, not complete)
This allows entrance through Windurst Walls.