I woudn’t bring anything to “sweeten” the bait. Bears get conditioned to a specific type of bait and a change can put them off for a while.
I never heard of vanilla on the Thermacell. I’d lean towards being scent free as possible.
Big bears usually have small looking ears that are on the side of their heads. Small bears have big “Mickey Mouse” ears on the top of their heads.
All bears look big at first. A really big bear will look HUGE!
Don’t shoot too soon. Luckily, bears usually stay around a bait for a while. That gives you plenty of time to get over the shakes and “bear fever”. Wait for a good shot and make it count. 
I don’t get to go until mid September. 
Good luck and post a story with some pics when you get back!