World number 11 Cibulkova has won eight career titles, including four in a stellar 2016, but is still seeking a breakthrough this year.
The 28-year-old was far too good for Mertens.
"After not an easy year for me, I'm finding my form. I'm really happy to start it here," Cibulkova said after advancing to her first final of 2017.
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Gavrilova had a tougher match against former world number two Radwanska.
Wearing her heart on her sleeve, an emotional Gavrilova used a powerful forehand to good effect, hitting a series of winners against her more stoic Polish opponent.
After nervously netting a forehand groundstroke to squander her first match point, Gavrilova made no mistake on her next chance to advance to her third career final.
"I trusted my game plan and I think I executed it very well," Gavrilova said.
"I was pretty aggressive and taking chances whenever I could on her second serve."
Heading into next week's U.S. Open, Saturday's Connecticut final will offer the 23-year-old Gavrilova a chance for her first career title.
(Reporting by Andrew Both in Cary, North Carolina; Editing by Ian Ransom)
