There are a few ways to get to Eldin Province. The one you'll use first is: in Faron Province, go past Coro (the lamp oil selling dude) and there should be an open gate. That will take you to Hyrule Field. Go east (west in wii) and there will be a path leading to another section of Hyrule field located in Eldin. There's also a bridge that leads from Eastern (western on Wii) Castle Town, but it's broken in the beginning of the game. And then there's the Bridge of Eldin, in the northern part of Hyrule, but it also breaks during the game. You might find this map helpful.