This can be a time consuming achievement, but very simple to complete. Here's the list of candy buckets you must visit:

Horde

1. Ashenvale, Splintertree Post
2. Barrens, Camp Taurajo
3. Barrens, Ratchet
4. Barrens, The Crossroads
5. Desolace, Shadowprey Village
6. Durotar, Razor Hill
7. Dustwallow Marsh, Brackenwall Village
8. Dustwallow Marsh, Mudsprocket
9. Feralas, Camp Mojache
10. Mulgore, Bloodhoof Village
11. Orgrimmar, Valley of Strength
12. Silithus, Cenarion Hold
13. Stonetalon Mountains, Sun Rock Retreat
14. Tanaris, Gadgetzan
15. Thunder Bluff, Lower Rise
16. Thousand Needles, Freewind Post
17. Winterspring, Everlook

One way to go about this is to start from Ratchet. If you follow this route, visit the following cities in this order:

1. Barrens, Ratchet
2. Barrens, The Crossroads
3. Barrens, Camp Taurajo
4. Dustwallow Marsh, Brackenwall Village
5. Dustwallow Marsh, Mudsprocket
6. Thousand Needles, Freewind Post
7. Tanaris, Gadgetzan
8. Silithus, Cenarion Hold
9. Feralas, Camp Mojache
10. Mulgore, Bloodhoof Village
11. Thunder Bluff, Lower Rise
12. Desolace, Shadowprey Village
13. Stonetalon Mountains, Sun Rock Retreat
14. Ashenvale, Splintertree Post
15. Winterspring, Everlook
16. Orgrimmar, Valley of Strength
17. Durotar, Razor Hill

Alliance

1. Ashenvale, Astranaar
2. Azuremyst Isle, Azure Watch
3. Barrens, Ratchet
4. Bloodmyst Isle, Blood Watch
5. Darkshore, Auberdine
6. Darnassus, Craftsmen's Terrace
7. Desolace, Nijel's Point
8. Dustwallow Marsh, Mudsprocket
9. Dustwallow Marsh, Theramore Isle
10. Exodar, Seat of the Naaru
11. Feralas, Feathermoon Stronghold
12. Silithus, Cenarion Hold
13. Stonetalon Mountains, Stonetalon Peak
14. Tanaris, Gadgetzan
15. Teldrassil, Dolanaar
16. Winterspring, Everlook

One way to go about this is to start from Ratchet. If you follow this route, visit the following cities in this order:

1. Barrens, Ratchet
2. Dustwallow Marsh, Theramore Isle
3. Dustwallow Marsh, Mudsprocket
4. Tanaris, Gadgetzan
5. Silithus, Cenarion Hold
6. Feralas, Feathermoon Stronghold
7. Desolace, Nijel's Point
8. Stonetalon Mountains, Stonetalon Peak
9. Ashenvale, Astranaar
10. Winterspring, Everlook
11. Darkshore, Auberdine
12. Azuremyst Isle, Azure Watch
13. Exodar, Seat of the Naaru
14. Darnassus, Craftsmen's Terrace
15. Teldrassil, Dolanaar