Cantina EnergyHere you get only 165 energy for free each day (120 accrued over time + 45 login bonus available), BUT you don't have to pay for node refreshes so you aren't limited to 5 attempts per day. For that reason, with Cantina Battles you won't use a strategy like for Fleet Battles or regular light side or dark side battles. Here you'll focus all your attempts on a single character until you reach a goal (which might not be 7*, there will often be intermediate goals), then move to the next goal on the priority list.
Priorities:
1. Mission Vao => 7*
2. T3-M4 => 7*
3. Geonosian Spy => 6*
4. Geonosian Soldier => 6*
5. Spy => 7*
6. Soldier => 7*
These farms will go quite quickly once Mission is done. Mission will only be slower because the cost per attempt is higher, so you'll get fewer attempts per day. But Geo Soldier will give you 20 attempts per day, which will yield an average of 12-14 shards per day. T3 and Spy are between those extremes.
By the way, when T3 is finished, it will be time to renumber your priority list and add some new things to the bottom so you always know where you're going. You shouldn't wait until you're done or nearly done with Spy & Soldier to start thinking about your next plan.
Regular Energy1. Jolee Bindo (DS: 6-D) => 7*, 16 energy/attempt, 80 energy/day
2. Zaalbar (LS: 5-D) => 7*, 16/attempt, 80/day
3. Hound's Tooth & Jango (LS 8-D) => 7* Hound's Tooth (Jango will be long done before then), 20/attempt, 100/day
4. Bossk (DS: 9-B) => 7*, 20/attempt, 100/day (NOTE: not available yet, node opens at level 85, but this is its priority)
5. Hyena Bomber ((DS: 8-B) => 7*, 20/attempt, 100/day
6. Vulture (LS: 4-D) => 7*, 12/attempt, 60/day
7. Jedi Knight Anakin (LS: 5-C) => 7*, 16/attempt, 80/day
8. Sabine Wren (DS: 1-A) => 7*, 12/attempt, 60/day
9. Xanadu Blood & Droideka (LS: 8-B) => Xanadu Blood 7* (Droideka will be 7* long before then), 20/attempt, 100/day
10. IG-2000 & Poggle (LS: 6-E) => IG-2000 7* (Poggle will be 7* long before then), 16/attempt, 80/day
You'll note that Bossk is on there even though his node is not yet available. That's fine. Just add it in when you can. Until then, as always, spend your energy right down the list every day until you run out. You should also be purchasing a 50-crystal regular energy refresh every single day. You might want to purchase 2 of those refreshes on some days, when you can afford it, just to keep things hurrying along.