It was a poor day on serve for the normally big-hitting Raonic. The 22-year-old from Thornhill, Ont., dropped four service games in a loss which took a mere 52 minutes.
The Bryans are bidding for a third consecutive final at the seaside Country Club. They beat the team of Toronto's Daniel Nestor and former partner Max Mirnyi for the 2012 title.
The young pair of Raonic and Tomic managed just five aces between them and converted on only one of five break point chances.
Raonic lost serve twice in the opening set as the experienced Bryan twins wrapped it up in 26 minutes.
In the second set, Raonic held to start the set and saved two match points in the final game — both of his serve.
But a winning Bryan return at the feet of Tomic ended the semifinal.
Despite the disappointment, Raonic will use the doubles as a spring board for his singles, where he is ranked 15th.
"It's fun for us, I like to play doubles with Bernie," said the Canadian. "It's a relaxed atmosphere.
"It also helps our singles and I hope it pays off. It's a type of tennis where you have to adapt and it can only help improve your singles on clay."
Raonic will take his game to his training base in Barcelona next week for that ATP clay event.